a(n) = 5^n - 4^n + 3^n.

Terms

a(0) =1a(1) =4a(2) =18a(3) =88a(4) =450a(5) =2344a(6) =12258a(7) =63928a(8) =331650a(9) =1710664a(10) =8776098a(11) =44810968a(12) =227894850a(13) =1155188584a(14) =5839863138a(15) =29458185208a(16) =148335970050a(17) =745888724104