a(n) = 2^(n-1)*(2^n+11).

Terms

a(0) =6a(1) =13a(2) =30a(3) =76a(4) =216a(5) =688a(6) =2400a(7) =8896a(8) =34176a(9) =133888a(10) =529920a(11) =2108416a(12) =8411136a(13) =33599488a(14) =134307840a(15) =537051136a(16) =2147844096a(17) =8590655488a(18) =34361180160a(19) =137441837056a(20) =549761581056