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Problem 656


Problem 656


Palindromic sequences

Given an irrational number $\alpha$, let $S_\alpha(n)$ be the sequence $S_\alpha(n)=\lfloor \alpha \cdot n \rfloor - \lfloor \alpha \cdot (n-1)\rfloor$ for $n\ge 1$.
($\lfloor \ldots \rfloor$ is the floor-function.)

It can be proven that for any irrational $\alpha$ there exist infinitely many values of $n$ such that the subsequence ${S_\alpha(1),S_\alpha(2)\ldots S_\alpha(n)}$ is palindromic.

The first $20$ values of $n$ that give a palindromic subsequence for $\alpha=\sqrt{31}$ are: $1$, $3$, $5$, $7$, $44$, $81$, $118$, $273$, $3158$, $9201$, $15244$, $21287$, $133765$, $246243$, $358721$, $829920$, $9600319$, $27971037$, $46341755$, $647124734.

Let $H_g(\alpha)$ be the sum of the first $g$ values of $n$ for which the corresponding subsequence is palindromic.
So $H_{20}(\sqrt{31})=150243655$.

Let $T={2, 3, 5, 6, 7, 8, 10, \ldots, 1000}$ be the set of positive integers, not exceeding $1000$, excluding perfect squares.
Calculate the sum of $H_{100}(\sqrt{\beta})$ for $\beta \in T$. Give the last $15$ digits of your answer.


回文序列

任取无理数$\alpha$,记$S_\alpha(n)$为序列$S_\alpha(n)=\lfloor \alpha \cdot n \rfloor - \lfloor \alpha \cdot (n-1)\rfloor$,其中$n\ge 1$。
($\lfloor \ldots \rfloor$表示下取整函数。)

可以证明,对于任意无理数$\alpha$,存在无数个$n$,使得子序列${S_\alpha(1),S_\alpha(2)\ldots S_\alpha(n)}$是回文的。

对于$\alpha=\sqrt{31}$,前$20$个满足上述条件的$n$分别是:$1$,$3$,$5$,$7$,$44$,$81$,$118$,$273$,$3158$,$9201$,$15244$,$21287$,$133765$,$246243$,$358721$,$829920$,$9600319$,$27971037$,$46341755$,$647124734$。

记$H_g(\alpha)$为前$g$个满足上述条件的$n$之和。
因此$H_{20}(\sqrt{31})=150243655$。

记$T={2, 3, 5, 6, 7, 8, 10, \ldots, 1000}$为不超过$1000$且不包含完全平方数的正整数所组成的集合。
对于所有$\beta \in T$,求$H_{100}(\sqrt{\beta})$之和,并给出最后$15$位数字作为你的答案。