a(n) = n*2^n - 2^(n/2)*sin(Pi*n/4).

Terms

a(0) =0a(1) =1a(2) =6a(3) =22a(4) =64a(5) =164a(6) =392a(7) =904a(8) =2048a(9) =4592a(10) =10208a(11) =22496a(12) =49152a(13) =106560a(14) =229504a(15) =491648a(16) =1048576a(17) =2227968a(18) =4718080a(19) =9960960a(20) =20971520a(21) =44041216a(22) =92276736a(23) =192940032a(24) =402653184a(25) =838856704a(26) =1744822272a(27) =3623870464a(28) =7516192768