diff --git a/151_paper_sheets.py b/151_paper_sheets.py
new file mode 100644
index 0000000..1e12f3a
--- /dev/null
+++ b/151_paper_sheets.py
@@ -0,0 +1,24 @@
+#!/usr/bin/env python3
+
+from fractions import Fraction
+
+def cut(state, i):
+    return state[:i] + (state[i]-1,) + \
+           tuple(n + 1 for n in state[i+1:])
+
+def search(state=(1, 0, 0, 0, 0), cache={}):
+    if state in cache:
+        return cache[state]
+    if sum(state) == state[-1] == 1:
+        return 1
+    r = 0
+    for i, p in enumerate(state):
+        if not p:
+            continue
+        r += Fraction(p, sum(state)) * \
+             search(cut(state, i), cache)
+    r += (sum(state) == 1)
+    cache[state] = r
+    return r
+
+print(float(round(search(), 6) - 2))
diff --git a/156_counting_digits.py b/156_counting_digits.py
new file mode 100644
index 0000000..bfda5eb
--- /dev/null
+++ b/156_counting_digits.py
@@ -0,0 +1,33 @@
+#!/usr/bin/env python3
+
+def calc(n, dig=1, verbose=False):
+    r = 0
+    for place in range(len(str(n))):
+        a = (n - (n % 10**(place+1))) // 10
+        b = 0
+        d = int(str(n)[-place-1])
+        if d == dig:
+            b = (n % 10**place) + 1
+        elif d > dig:
+            b = 10**place
+        if verbose:
+            print(place, a, b, a+b)
+        r += a + b
+    return r
+
+def search(dig, pw=2, num=0):
+    if pw == 0:
+        return sum(num + d for d in range(10) if num+d == calc(num+d, dig))
+    r = 0
+    for d in range(10):
+        newnum = num + d * 10**pw
+        maxnum = num + (d + 1) * 10**pw - 1
+        if maxnum < calc(newnum, dig):
+            continue
+        if calc(maxnum, dig) < newnum:
+            continue
+        r += search(dig, pw-1, newnum)
+    return r
+
+depth = 10
+print(sum(search(d, depth) for d in range(1, 10)))
diff --git a/158_strings.py b/158_strings.py
new file mode 100644
index 0000000..cbda358
--- /dev/null
+++ b/158_strings.py
@@ -0,0 +1,18 @@
+#!/usr/bin/env python3
+
+from math import factorial
+
+def bin(n, k):
+    if k > n:
+        return 0
+    return factorial(n) // (factorial(n-k)*factorial(k))
+
+def strings(k):
+    k -= 2
+    s = 0
+    for inter in range(25):
+        for i in range(0,k+1):
+            s += (25-inter) * 2**i * bin(inter, i) * bin(24-inter, k-i)
+    return s
+
+print(max((2**k - k - 1) * bin(26, k) for k in range(2, 27)))
diff --git a/160_factorial_trailing_digits.py b/160_factorial_trailing_digits.py
new file mode 100644
index 0000000..49c8882
--- /dev/null
+++ b/160_factorial_trailing_digits.py
@@ -0,0 +1,41 @@
+#!/usr/bin/env python3
+
+from math import log
+
+digs = 5
+mask = 10**digs
+
+sieve = [1] * mask
+for n in range(1, mask):
+    if n%2 and n%5:
+        sieve[n] = (sieve[n-1] * n) % mask
+    else:
+        sieve[n] = sieve[n-1]
+
+def numf(n, N):
+    return sum(N // (n**pw) for pw in range(1, int(log(N) / log(n))+1))
+
+def numof2(N):
+    return numf(2, N) - numf(5, N)
+
+def roots(N):
+    a = 1
+    while a <= N:
+        b = 1
+        while a * b <= N:
+            yield a * b
+            b *= 2
+        a *= 5
+
+def main(N):
+    r = 1
+    p = sieve[-1]
+    for root in roots(N):
+        d = N // root
+        r *= pow(p, d // mask, mask)
+        r *= sieve[d % mask]
+        r %= mask
+    r *= pow(2, numof2(N), mask)
+    return r % mask
+
+print(main(10**12))
diff --git a/162_hexadecimal_numbers.py b/162_hexadecimal_numbers.py
new file mode 100644
index 0000000..89a61bd
--- /dev/null
+++ b/162_hexadecimal_numbers.py
@@ -0,0 +1,30 @@
+#!/usr/bin/env python3
+
+from itertools import product
+from math import factorial
+
+def bin(n, k):
+    return factorial(n) // (factorial(n-k) * factorial(k))
+
+digs = list(map(str, range(10))) + list("ABCDEF")
+cache = {val : {0 : all(val)} for val in product([True, False], repeat=3)}
+
+def f(i, flags=(False, False, False), fst=1):
+    if i in cache[flags] and (not fst or not i):
+        return cache[flags][i]
+    r = 13 * f(i-1, flags, 0)
+    r += sum(f(i-1, flags[:n] + (True,) + flags[n+1:], 0) for n in range(fst, 3))
+    if not fst:
+        cache[flags][i] = r
+    return r
+
+def dec2hex(n):
+    r = str()
+    while n:
+        r = r + digs[n % 16]
+        n //= 16
+    return r[::-1]
+
+r = sum(f(i) for i in range(1, 17))
+
+print(dec2hex(r))
diff --git a/164_numbers_consecutive_digits.py b/164_numbers_consecutive_digits.py
new file mode 100644
index 0000000..c771021
--- /dev/null
+++ b/164_numbers_consecutive_digits.py
@@ -0,0 +1,12 @@
+#!/usr/bin/env python3
+
+cache = [[{0 : 1} for b in range(10)] for a in range(10)]
+
+def f(i, a=0, b=0, fst=1):
+    if i in cache[a][b]:
+        return cache[a][b][i]
+    r = sum((f(i-1, b, n, 0) for n in range(fst, 10-a-b)))
+    cache[a][b][i] = r
+    return r
+
+print(f(20))
diff --git a/165_intersections.py b/165_intersections.py
new file mode 100644
index 0000000..2e04b72
--- /dev/null
+++ b/165_intersections.py
@@ -0,0 +1,48 @@
+#!/usr/bin/env python3
+
+from fractions import Fraction
+from itertools import combinations
+
+def solve(line1, line2):
+    x1, y1 = line1[0][0] - line1[1][0], line1[0][1] - line1[1][1]
+    x2, y2 = -line2[0][0] + line2[1][0], -line2[0][1] + line2[1][1]
+    xv, yv = line2[1][0] - line1[1][0], line2[1][1] - line1[1][1]
+    det = x1*y2 - y1*x2
+    if det == 0:
+        return None
+    p = det // abs(det)
+    det = abs(det)
+    n = p * (xv*y2 - yv*x2)
+    if not (0 < n < det) or not (0 < p * (x1*yv - y1*xv) < det):
+        return None
+    return (line1[1][0] + Fraction(n, det) * x1, line1[1][1] + Fraction(n, det) * y1)
+
+l1 = (27, 44), (12, 32)
+l2 = (46, 53), (17, 62)
+l3 = (46, 70), (22, 40)
+
+
+def blum(n):
+    s = 290797
+    for i in range(n):
+        s = pow(s, 2, 50515093)
+        yield s % 500
+
+N = 5000
+nums = list(blum(N*4))
+lines = []
+
+for i in range(0, len(nums)-3, 4):
+    line = (nums[i], nums[i+1]), (nums[i+2], nums[i+3])
+    lines.append(line)
+
+points = []
+
+for a, b in combinations(lines, 2):
+    p = solve(a, b)
+    if p == None:
+        continue
+    points.append(p)
+
+
+print(len(set(points)))
diff --git a/168_number_rotations.py b/168_number_rotations.py
new file mode 100644
index 0000000..e3b9aaa
--- /dev/null
+++ b/168_number_rotations.py
@@ -0,0 +1,22 @@
+#!/usr/bin/env python3
+
+def search(i, k, fst, dig=None, r=0, num=str()):
+    if dig == None:
+        dig = fst
+    if i == 0:
+        return False
+    n = k*dig + r
+    if n < 10 and fst == n and dig != 0:
+        return str(dig) + num
+    return search(i-1, k, fst, n%10, n//10, str(dig) + num)
+
+places = 100
+s = 0
+for k in range(1, 10):
+    for dig in range(1, 10):
+        n = search(places, k, dig)
+        if n:
+            r = places // len(n)
+            for i in range((1 + (len(n)==1)), r+1):
+                s += int(i*n) % 10**5
+print(s % 10**5)
diff --git a/171_finding_numbers.py b/171_finding_numbers.py
new file mode 100644
index 0000000..3e0c909
--- /dev/null
+++ b/171_finding_numbers.py
@@ -0,0 +1,20 @@
+#!/usr/bin/env python3
+
+from math import ceil
+
+digs = 20
+ln = 9**2 * digs + 1
+mod = 10**9
+
+
+sums = [0] * ln
+count = [1] + [0] * (ln - 1)
+
+for pw in range(digs):
+    for dsum in range(9**2 * pw, -1, -1):
+        for dig in range(1, 10):
+            sums[dsum + dig**2] += dig * 10**pw * count[dsum] + sums[dsum]
+            count[dsum + dig**2] += count[dsum]
+
+
+print(sum(sums[i**2] for i in range(int(ceil(ln**0.5)))) % mod)
diff --git a/173_square_laminae.py b/173_square_laminae.py
new file mode 100644
index 0000000..40b6866
--- /dev/null
+++ b/173_square_laminae.py
@@ -0,0 +1,9 @@
+#!/usr/bin/env python3
+
+from math import sqrt
+
+b = 10**6
+t = 0
+for n in range(1, b//4):
+    t += int(sqrt(b + n**2) - n)//2
+print(t)
diff --git a/174_square_laminae.py b/174_square_laminae.py
new file mode 100644
index 0000000..f2d2452
--- /dev/null
+++ b/174_square_laminae.py
@@ -0,0 +1,18 @@
+#!/usr/bin/env python3
+
+def divisors(n):
+    sieve = [1]*n
+    for p in range(2, n):
+        if sieve[p] > 1:
+            continue
+        pw = 1
+        while p**pw < n:
+            for i in range(p**pw, n, p**pw):
+                sieve[i] *= (pw+1)
+                sieve[i] //= pw
+            pw += 1
+    return sieve
+
+n = 10**6 // 4
+divs = divisors(n+1)
+print(len([0 for i in divs if 0 < i//2 <= 10]))
diff --git a/178_step_numbers.py b/178_step_numbers.py
new file mode 100644
index 0000000..db6551a
--- /dev/null
+++ b/178_step_numbers.py
@@ -0,0 +1,42 @@
+#!/usr/bin/env python3
+
+conds = ["any", "both", "nine"]
+
+cache = {c : {n : dict() for n in range(10)} for c in conds}
+
+def f(n, i, contains = "both"):
+    if i in cache[contains][n]:
+        return cache[contains][n][i]
+
+    if i == 1:
+        if contains == "both":
+            r = 0
+        elif contains == "any":
+            r = 1
+        elif contains == "nine":
+            r = (n == 9)
+        cache[contains][n][i] = r
+        return r
+
+    g = lambda x,y: f(x, i-1, y)
+
+    flag = contains
+
+    if n == 0 or n == 9:
+        if contains == "both":
+            flag = "nine"
+        elif contains == "nine" and n == 9:
+            flag = "any"
+        r = g(1, flag)
+    else:
+        r = g(n-1, contains) + g(n+1, contains)
+
+    cache[contains][n][i] = r
+    return r
+
+places = 40
+s = 0
+
+for p in range(1, places+1):
+    s += sum(f(n, p) for n in range(1,10))
+print(s)
diff --git a/179_consecutive_positive_divisors.py b/179_consecutive_positive_divisors.py
new file mode 100644
index 0000000..af7dbf0
--- /dev/null
+++ b/179_consecutive_positive_divisors.py
@@ -0,0 +1,13 @@
+#!/usr/bin/env python3
+
+lim = 10**7
+divcount = [1]*lim
+count = 0
+
+for n in range(2, lim):
+    for i in range(n, lim, n):
+        divcount[i] += 1
+    if divcount[n] == divcount[n-1]:
+        count += 1
+
+print(count)
diff --git a/187_semiprimes.py b/187_semiprimes.py
new file mode 100644
index 0000000..27bc9fe
--- /dev/null
+++ b/187_semiprimes.py
@@ -0,0 +1,20 @@
+#!/usr/bin/env python3
+
+def primes(n):
+    count = 0
+    sieve = [False]*n
+    for p in range(2, n):
+        if sieve[p]:
+            continue
+        for i in range(p**2, n, p):
+            sieve[i] = True
+        np = 2*p
+        for p2 in range(2,p+1):
+            if np >= n:
+                break
+            if not sieve[p2]:
+                count += 1
+            np += p
+    return count
+
+print(primes(10**8))
diff --git a/188_the_hyperexponentiation_of_a_number.py b/188_the_hyperexponentiation_of_a_number.py
new file mode 100644
index 0000000..6ac3e39
--- /dev/null
+++ b/188_the_hyperexponentiation_of_a_number.py
@@ -0,0 +1,11 @@
+#!/usr/bin/env python3
+
+a = 1777
+k = 1855
+
+n = 1
+
+for i in range(k):
+    n = pow(a, n, 10**8)
+
+print(n)
diff --git a/191_prize_strings.py b/191_prize_strings.py
new file mode 100644
index 0000000..d27145c
--- /dev/null
+++ b/191_prize_strings.py
@@ -0,0 +1,26 @@
+#!/usr/bin/env python3
+
+from math import factorial
+
+def bin(n, k):
+    return factorial(n) // (factorial(n-k) * factorial(k))
+
+def late(n):
+    return 3**n - 2**n - 2**(n-1) * n
+
+def absent2(n):
+    if n < 3:
+        return 0
+    middle = (n-3) * 2**(n-4) - sum(2**(n-4-i) * absent(i) for i in range(n-3))
+    left  = sum(2**(n-4-i) * (i * 2**(i-1)  -  absent2(i)) for i in range(n-3))
+    right = (n-3) * 2**(n-4) + sum((n-3-i) * 2**(n-4-i) * (2**(i-1)  -  absent(i-1)) for i in range(1, n-3))
+    return right + left + middle
+
+def absent(n):
+    if n < 3:
+        return 0
+    return 2**(n-3) + (n-3) * 2**(n-4) - sum(2**(n-4-i) * absent(i) for i in range(n-3))
+
+n = 30
+
+print(int(3**n - late(n) - absent(n) - absent2(n)))
diff --git a/193_squarefree_numbers.py b/193_squarefree_numbers.py
new file mode 100644
index 0000000..828545d
--- /dev/null
+++ b/193_squarefree_numbers.py
@@ -0,0 +1,25 @@
+#!/usr/bin/env python3
+
+def primes(n):
+    sieve = [False] * n
+    yield 2
+    for p in range(3, n, 2):
+        if sieve[p]:
+            continue
+        for i in range(p**2, n, 2*p):
+            sieve[i] = True
+        yield p
+
+def search(i=0, n=1, sign=1):
+    r = 0
+    while squares[i] * n <= N:
+        m = n * squares[i]
+        r += sign * (N // m)
+        r += search(i+1, m, sign * (-1))
+        i += 1
+    return r
+
+N = 2**50
+squares = [p**2 for p in primes(2**25)] + [N+1]
+
+print(N - search())