CF1957E Carousel of Combinations
Description
You are given an integer $ n $ . The function $ C(i,k) $ represents the number of distinct ways you can select $ k $ distinct numbers from the set { $ 1, 2, \ldots, i $ } and arrange them in a circle $ ^\dagger $ .
Find the value of
$$
\sum\limits_{i=1}^n \sum\limits_{j=1}^i \left( C(i,j) \bmod j \right)
$$
Here, the operation $ x \\bmod y $ denotes the remainder from dividing $ x $ by $ y $ .
Since this value can be very large, find it modulo $ 10^9+7 $ .
$ ^\\dagger $ In a circular arrangement, sequences are considered identical if one can be rotated to match the other. For instance, $ \[1, 2, 3\] $ and $ \[2, 3, 1\]$$$ are equivalent in a circle.
Input Format
The first line contains a single integer $ t $ ( $ 1 \leq t \leq 10^5 $ ) — the number of test cases.
The only line of each test case contains a single integer $ n $ ( $ 1 \le n \le 10^6 $ ).
Output Format
For each test case, output a single integer on a new line — the value of the expression to be calculated modulo $ 10^9+7 $ .
Explanation/Hint
In the first test case, $ C(1,1) \bmod 1 = 0 $ .
In the second test case:
- $ C(1,1)=1 $ (the arrangements are: $ [1] $ );
- $ C(2,1)=2 $ (the arrangements are: $ [1] $ , $ [2] $ );
- $ C(2,2)=1 $ (the arrangements are: $ [1, 2] $ );
- $ C(3,1)=3 $ (the arrangements are: $ [1] $ , $ [2] $ , $ [3] $ );
- $ C(3,2)=3 $ (the arrangements are: $ [1, 2] $ , $ [2, 3] $ , $ [3, 1] $ );
- $ C(3,3)=2 $ (the arrangements are: $ [1, 2, 3] $ , $ [1, 3, 2] $ ).
In total, $ \left(C(1,1) \bmod 1\right) + \left(C(2,1) \bmod 1\right) + \left(C(2,2) \bmod 2\right) + \left(C(3,1) \bmod 1\right) + \left(C(3,2) \bmod 2\right) + \left(C(3,3) \bmod 3\right) = 4 $ .