12n+7^n+5^n.

Terms

a(0) =2a(1) =24a(2) =98a(3) =504a(4) =3074a(5) =19992a(6) =133346a(7) =901752a(8) =6155522a(9) =42306840a(10) =292240994a(11) =2026155000a(12) =14085427970a(13) =98109713688a(14) =684326588642