Подскажите, как сократить время работы программы?
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Edited by moderator 19.11.2019 23:42

Take a look at https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes.

First you should rewrite function which counts sum of divisors: for (i=2;i*i<=n;i++)...,
second you shouldn't compute triviality of all numbers in [i,j]: just for numbers from j downto first prime number>=i, and of course take into account that triviality(1)=0.