1,1,2.3,5.......

what can be the general term for this?

Assuming that's 1, 1, 2, 3, 5... it's the Fibonacci sequence, in which X(i) = X(i-1) + X(i-2), where X(1) = X(2) = 1. So 1+1=2, 1+2=3, 2+3=5, 3+5=8, 5+8=13 etc etc.