Koobits Math: Olympiad
Problem 1 (Number theory — easy) Find all integers n such that n^2 + n is even. Solution: n^2 + n = n(n+1) is product of consecutive integers, so one is even → product even for all integers n. Thus all integers n.
Problem 1 (Number theory — easy) Find all integers n such that n^2 + n is even. Solution: n^2 + n = n(n+1) is product of consecutive integers, so one is even → product even for all integers n. Thus all integers n.