17 lines
378 B
Python
17 lines
378 B
Python
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#!/usr/bin/env python3
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# closed form expression, d = digits
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# if d is even: 20 * 30**(d/2 - 1)
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# if d = 3+4n : 5 * 20**((d+1)/4) * 25**((i-3)/4)
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# iterate all digits in range
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def main(d): #inclusive
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r = 0
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for i in range(2,d+1,2):
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r += 20*30**(i//2 - 1)
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for i in range(3,d+1,4):
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r += 5 * 20**((i+1)//4) * 25**((i-3)//4)
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return r
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print(main(9))
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