(1/4) times the sum of the elements of all subsets of [n] whose sum is divisible by four.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =4a(5) =14a(6) =42a(7) =112a(8) =288a(9) =720a(10) =1760a(11) =4224a(12) =9984a(13) =23296a(14) =53760a(15) =122880a(16) =278528a(17) =626688a(18) =1400832a(19) =3112960a(20) =6881280a(21) =15138816a(22) =33161216a(23) =72351744a(24) =157286400a(25) =340787200a(26) =736100352a(27) =1585446912a(28) =3405774848a(29) =7298088960