a(n) = Sum_{k=0..n} C(n,3k+2)^2.

Terms

a(0) =0a(1) =0a(2) =1a(3) =9a(4) =36a(5) =101a(6) =261a(7) =882a(8) =3921a(9) =17253a(10) =67554a(11) =243695a(12) =876789a(13) =3324906a(14) =13166791a(15) =52301709a(16) =203824548a(17) =782913717a(18) =3010327497a(19) =11695756698a(20) =45823049817a(21) =179787741723a(22) =703527078258