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

Terms

a(0) =1a(1) =3a(2) =9a(3) =26a(4) =72a(5) =192a(6) =496a(7) =1248a(8) =3072a(9) =7424a(10) =17664a(11) =41472a(12) =96256a(13) =221184a(14) =503808a(15) =1138688a(16) =2555904a(17) =5701632a(18) =12648448a(19) =27918336a(20) =61341696a(21) =134217728a(22) =292552704a(23) =635437056a(24) =1375731712a(25) =2969567232a(26) =6392119296a(27) =13723762688