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Problem 805


Problem 805


Shifted Multiples

For a positive integer n, let s(n) be the integer obtained by shifting the leftmost digit of the decimal representation of n to the rightmost position.

For example, s(142857)=428571 and s(10)=1.

For a positive rational number r, we define N(r) as the smallest positive integer n such that s(n)=rn.

If no such integer exists, then N(r) is defined as zero.

For example, N(3)=142857, N(110)=10 and N(2)=0.

Let T(M) be the sum of N(u3/v3) where (u,v) ranges over all ordered pairs of coprime positive integers not exceeding M.

For example, T(3)262429173(mod1 000 000 007).

Find T(200). Give your answer modulo 1 000 000 007.


数字轮转倍数

对于正整数n,记s(n)为将n的十进制表示下最左侧数字移到最右侧所得到的数。

例如,s(142857)=428571s(10)=1

对于正有理数r,定义N(r)为满足s(n)=rn的最小正整数n

若不存在这样的正整数,则N(r)取零。

例如,N(3)=142857N(110)=10N(2)=0

对于所有不超过M的互质正整数对(u,v),记T(M)为所有N(u3/v3)之和。

例如,T(3)262429173(mod1 000 000 007)

T(200),并将你的答案对1 000 000 007取余。


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