x->x/2 if x even, x->3x-1 if x odd.

Terms

a(0) =90a(1) =45a(2) =134a(3) =67a(4) =200a(5) =100a(6) =50a(7) =25a(8) =74a(9) =37a(10) =110a(11) =55a(12) =164a(13) =82a(14) =41a(15) =122a(16) =61a(17) =182a(18) =91a(19) =272a(20) =136a(21) =68a(22) =34a(23) =17a(24) =50a(25) =25a(26) =74a(27) =37a(28) =110a(29) =55