43 lines
743 B
Python
43 lines
743 B
Python
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#!/usr/bin/env python3
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def primes(n):
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sieve = [True] * n
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for p in range(2, int(n**0.5)):
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if not sieve[p]:
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continue
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for i in range(p**2, n, p):
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sieve[i] = False
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return [False, False] + sieve[2:]
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def is_prime(p):
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if p >= len(sieve):
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raise LimitError
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return sieve[p]
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def getnum(n, c):
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m = n//6
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if c:
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return 3*(m-1)*m + 2
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return 3*m*(m+1) + 1
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sieve = primes(10**6)
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target = 2000
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c = 2
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n = 6
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while c < target:
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n += 6
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if not is_prime(n-1):
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continue
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c += is_prime(n+1) and is_prime(2*n + 5)
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if c == target:
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flag = True
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break
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c += is_prime(n+5) and is_prime(2*n-7)
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else:
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flag = False
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print(getnum(n, flag))
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