Those 4 terms are: 21,32,24,33 So we assume it continues like this: 21,32,24,33,25,36,28,37,29,310,212,311,213,314,216,315. General term for k=1,2,3,... a4k-3 = 24k-3, a4k-2 = 34k-2, a4k-3 = 24k, a4k = 34k-3,... Edwin