a(n) = floor(binomial(n+7,7)/binomial(n+3,3)).

Terms

a(0) =1a(1) =2a(2) =3a(3) =6a(4) =9a(5) =14a(6) =20a(7) =28a(8) =39a(9) =52a(10) =68a(11) =87a(12) =110a(13) =138a(14) =171a(15) =209a(16) =253a(17) =303a(18) =361a(19) =427a(20) =501a(21) =585a(22) =678a(23) =783a(24) =899a(25) =1027a(26) =1169a(27) =1325a(28) =1496a(29) =1683