a(n) = 2*3^n + 4^n + 3*n.

Terms

a(0) =3a(1) =13a(2) =40a(3) =127a(4) =430a(5) =1525a(6) =5572a(7) =20779a(8) =78682a(9) =301537a(10) =1166704a(11) =4548631a(12) =17840134a(13) =70297549a(14) =278001436a(15) =1102439683a(16) =4381060786a(17) =17438149561a(18) =69494317768a(19) =277202429935