a(n) = (n^2/8+3*n/8-2)*2^n + 3.

Terms

a(0) =0a(1) =0a(2) =5a(3) =27a(4) =99a(5) =307a(6) =867a(7) =2307a(8) =5891a(9) =14595a(10) =35331a(11) =83971a(12) =196611a(13) =454659a(14) =1040387a(15) =2359299a(16) =5308419a(17) =11862019a(18) =26345475a(19) =58195971a(20) =127926275a(21) =279969795a(22) =610271235a(23) =1325400067a(24) =2868903939a(25) =6190792707a(26) =13321109507a(27) =28588376067a(28) =61203283971a(29) =130728067075