a(n) = Sum_{k=0..floor(2*n/7)} binomial(2*k+1,2*n-7*k).

Terms

a(0) =1a(1) =0a(2) =0a(3) =0a(4) =3a(5) =1a(6) =0a(7) =1a(8) =10a(9) =5a(10) =0a(11) =7a(12) =35a(13) =21a(14) =2a(15) =36a(16) =126a(17) =84a(18) =20a(19) =165a(20) =462a(21) =331a(22) =133a(23) =716a(24) =1716a(25) =1302a(26) =741a(27) =3016a(28) =6436a(29) =5141