a(n) = Sum_{k=0..floor(n/7)} binomial(n-4*k,3*k).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =1a(6) =1a(7) =2a(8) =5a(9) =11a(10) =21a(11) =36a(12) =57a(13) =85a(14) =122a(15) =173a(16) =249a(17) =371a(18) =575a(19) =918a(20) =1485a(21) =2398a(22) =3830a(23) =6030a(24) =9369a(25) =14422a(26) =22107a(27) =33909a(28) =52226a(29) =80888