Sequences 1 + 2 + 3 + .....+ N = (N*(N+1))/2 1 + 2^2 + 3^2 + .... + N^2 = (N*(N+1)*(2N+1))/6 Permutaion && Combination NPR = N! / (N-R)! NCR = N! / ((N-R)! x R!) NC2 = (N * (N-1 ))/ 2