4^n+3n5^(n-1).

Terms

a(0) =1a(1) =7a(2) =46a(3) =289a(4) =1756a(5) =10399a(6) =60346a(7) =344509a(8) =1940536a(9) =10809019a(10) =59642326a(11) =326459929a(12) =1774589716a(13) =9588593239a(14) =51537966706a(15) =275731944949