a(n) = 4^n + 6^n.

Terms

a(0) =2a(1) =10a(2) =52a(3) =280a(4) =1552a(5) =8800a(6) =50752a(7) =296320a(8) =1745152a(9) =10339840a(10) =61514752a(11) =366991360a(12) =2193559552a(13) =13127802880a(14) =78632599552a(15) =471258726400