27 lines
725 B
Python
27 lines
725 B
Python
#!/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)))
|