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Problem 618


Problem 618


Numbers with a given prime factor sum

Consider the numbers 15, 16 and 18:
15=3×5 and 3+5=8.
16=2×2×2×2 and 2+2+2+2=8.
18=2×3×3 and 2+3+3=8.
15, 16 and 18 are the only numbers that have 8 as sum of the prime factors (counted with multiplicity).

We define S(k) to be the sum of all numbers n where the sum of the prime factors (with multiplicity) of n is k.
Hence S(8)=15+16+18=49.
Other examples: S(1)=0, S(2)=2, S(3)=3, S(5)=5+6=11.

The Fibonacci sequence is F1=1, F2=1, F3=2, F4=3, F5=5,
Find the last nine digits of k=224S(Fk).


给定质因数和的整数

考虑整数15,16和18的质因数分解:
15=3×5,而3+5=8
16=2×2×2×2,而2+2+2+2=8
18=2×3×3,而2+3+3=8
15,16和18是仅有的质因数和(包括重复)为8的整数。

S(k)为所有质因数和(包括重复)为k的整数n的和。
因此S(8)=15+16+18=49
其它例子包括:S(1)=0S(2)=2S(3)=3S(5)=5+6=11

考虑斐波那契数列F1=1F2=1F3=2F4=3F5=5
k=224S(Fk)的最后九位数字。


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