a(n) = 4^n*(n^2 - n + 32)/32.

Terms

a(0) =1a(1) =4a(2) =17a(3) =76a(4) =352a(5) =1664a(6) =7936a(7) =37888a(8) =180224a(9) =851968a(10) =3997696a(11) =18612224a(12) =85983232a(13) =394264576a(14) =1795162112a(15) =8120172544a(16) =36507222016a(17) =163208757248a(18) =725849473024