a(n) = 7^n+4^n-1^n.

Terms

a(0) =1a(1) =10a(2) =64a(3) =406a(4) =2656a(5) =17830a(6) =121744a(7) =839926a(8) =5830336a(9) =40615750a(10) =283523824a(11) =1981521046a(12) =13858064416a(13) =96956119270a(14) =678491508304