| 2024 China Collegiate Programming Contest (CCPC) Jinan Site (The 3rd Universal Cup. Stage 17: Jinan) |
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The renowned alchemist Xu Dog discovered that precisely removing impurities could enhance the spiritual essence of the elixirs he was refining. Through day after day of alchemy, he found that the nature of these impurities was intricately related to mathematical problems. Since your progress in Dao is still shallow, Xu Dog decided to tell you the mathematical problem he needs to solve in the most straightforward way, rather than through the esoteric problems of alchemy.
Given two positive integers $$$n \leq m$$$, calculate the sum of the answers to the following problem for all subsets of size $$$n$$$ of $$$\{1, 2, \dots, m\}$$$, modulo $$$998\,244\,353$$$:
The greatest common divisor of a set is defined as the largest value among the common divisors of all elements in the set. For example, the greatest common divisor of the set $$$\{6, 9, 15\}$$$ is $$$3$$$.
Input consists of a single line containing two integers $$$m, n~ (1 \leq n \leq m \leq 10 ^ 5)$$$.
Output an integer representing the answer, modulo $$$998\,244\,353$$$.
4 3
7
11 4
1187
100000 99999
17356471
For the first example, all cases are listed below:
Therefore, the answer is $$$2 + 0 + 2 + 3 \bmod 998\,244\,353 = 7$$$.
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