a(n) = (6^n - 5^n - 4^n - 3^n + 4*2^n)/2.

Terms

a(0) =1a(1) =1a(2) =1a(3) =16a(4) =199a(5) =1756a(6) =13231a(7) =91876a(8) =608959a(9) =3922396a(10) =24798511a(11) =154802836a(12) =957674719a(13) =5885660236a(14) =35993747791a(15) =219289723396