Questions On GCD(Euclid's Algorithm), Modular properties, Fermat's little theorem, modular exponentiation Codechef FLOW016 - GCD and LCM Codechef GCDQ - GCD Queries Codechef GCD2 - GCD2 Spoj MARBLES - Marbles Spoj LCMSUM - LCM Sum Hackerearth - Shantam and Richness Hackerearth - Panda and Chain Reaction Hackerearth - Selection of Cities Hackerearth - Calculate the Power Hackerearth - Unlock the Door Codeforces - Beautiful Numbers Codeforces - Dima and Sequence Codeforces - Nastya and a Wardrobe Codeforces - Max History Some Reading material Basics of Number Theory Proof of Euclid's Algorithm Proofs of Fermat's little theorem