a(n) = 2*(4 + 17*2^(n-1)).

Terms

a(0) =25a(1) =42a(2) =76a(3) =144a(4) =280a(5) =552a(6) =1096a(7) =2184a(8) =4360a(9) =8712a(10) =17416a(11) =34824a(12) =69640a(13) =139272a(14) =278536a(15) =557064a(16) =1114120a(17) =2228232a(18) =4456456a(19) =8912904a(20) =17825800a(21) =35651592a(22) =71303176a(23) =142606344a(24) =285212680a(25) =570425352a(26) =1140850696a(27) =2281701384a(28) =4563402760a(29) =9126805512