a(n) = 3^n + n^2.

Terms

a(0) =1a(1) =4a(2) =13a(3) =36a(4) =97a(5) =268a(6) =765a(7) =2236a(8) =6625a(9) =19764a(10) =59149a(11) =177268a(12) =531585a(13) =1594492a(14) =4783165a(15) =14349132a(16) =43046977a(17) =129140452a(18) =387420813a(19) =1162261828a(20) =3486784801a(21) =10460353644a(22) =31381060093a(23) =94143179356a(24) =282429537057a(25) =847288610068