a(n) = (19*5^n - 16*3^n + 1) / 4.

Terms

a(0) =1a(1) =12a(2) =83a(3) =486a(4) =2645a(5) =13872a(6) =71303a(7) =362346a(8) =1829225a(9) =9198612a(10) =46150523a(11) =231225006a(12) =1157542205a(13) =5791962552a(14) =28972567343a(15) =144901100466a(16) =724620293585