a(n) = Sum_{k=0..floor(3*n/14)} binomial(3*n-13*k,k).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =3a(6) =6a(7) =9a(8) =12a(9) =15a(10) =24a(11) =42a(12) =69a(13) =105a(14) =151a(15) =224a(16) =351a(17) =559a(18) =875a(19) =1331a(20) =2009a(21) =3071a(22) =4760a(23) =7400a(24) =11417a(25) =17486a(26) =26768a(27) =41153a(28) =63504a(29) =97979