a(n) = 3*2^n + 3*4^n + 6^(n+1) + 1.

Terms

a(0) =13a(1) =55a(2) =277a(3) =1513a(4) =8593a(5) =49825a(6) =292417a(7) =1729153a(8) =10275073a(9) =61254145a(10) =365945857a(11) =2189371393a(12) =13111037953a(13) =78565515265a(14) =470990340097