a(n) = Sum_{k=0..floor(n/3)} binomial(k,3*n-9*k).

Terms

a(0) =1a(1) =0a(2) =0a(3) =1a(4) =0a(5) =0a(6) =1a(7) =0a(8) =0a(9) =1a(10) =1a(11) =0a(12) =1a(13) =4a(14) =0a(15) =1a(16) =10a(17) =0a(18) =1a(19) =20a(20) =1a(21) =1a(22) =35a(23) =7a(24) =1a(25) =56a(26) =28a(27) =1a(28) =84a(29) =84