27 lines
725 B
Python
27 lines
725 B
Python
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#!/usr/bin/env python3
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from math import factorial
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def bin(n, k):
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return factorial(n) // (factorial(n-k) * factorial(k))
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def late(n):
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return 3**n - 2**n - 2**(n-1) * n
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def absent2(n):
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if n < 3:
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return 0
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middle = (n-3) * 2**(n-4) - sum(2**(n-4-i) * absent(i) for i in range(n-3))
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left = sum(2**(n-4-i) * (i * 2**(i-1) - absent2(i)) for i in range(n-3))
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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))
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return right + left + middle
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def absent(n):
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if n < 3:
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return 0
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return 2**(n-3) + (n-3) * 2**(n-4) - sum(2**(n-4-i) * absent(i) for i in range(n-3))
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n = 30
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print(int(3**n - late(n) - absent(n) - absent2(n)))
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