a(n) = Sum_{k=0..n} (k+1) * binomial(k,4*(n-k)).

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =5a(5) =11a(6) =37a(7) =113a(8) =289a(9) =640a(10) =1280a(11) =2412a(12) =4468a(13) =8429a(14) =16460a(15) =33062a(16) =67084a(17) =135283a(18) =268929a(19) =526680a(20) =1020344a(21) =1966429a(22) =3787730a(23) =7309799a(24) =14135460a(25) =27353769a(26) =52882135a(27) =102017609a(28) =196309933a(29) =376896805