Resource

Firstly You need to get comfortable with these topics primarily

Divisibility Congruence, residue classes, Primes, properties of primes, prime power factorization, gcd, properties of gcd, lcm, Euclid's algorithm for gcd, and extended Euclid for linear diophantine equations, Chinese remainder theorem, Number Systems in different bases, and related properties,

Here are some algorithms you would need to know — Bigmod (fast exponentiation under modulo) — Inverse mod (conditions for existence) — Sieve for precalculation of primes — Factorization, prime-power factorization

Resources: 1.Blog/Site-- https://forthright48.com/p-cpps-101/ https://cp-algorithms.com/index.html 2:Youtube-- https://www.youtube.com/watch?v=dg1CUYrLrD0&list=PL5DyztRVgtRWblnyEHtajWijQffrfwLz6