a(n) = (2+3^n)*(3+2^n).

Terms

a(0) =12a(1) =25a(2) =77a(3) =319a(4) =1577a(5) =8575a(6) =48977a(7) =286759a(8) =1699817a(9) =10137775a(10) =60645377a(11) =363332599a(12) =2178384857a(13) =13065493375a(14) =78378545777a(15) =470228096839