a(n) = 21*binomial(n+6,7).

Terms

a(0) =0a(1) =21a(2) =168a(3) =756a(4) =2520a(5) =6930a(6) =16632a(7) =36036a(8) =72072a(9) =135135a(10) =240240a(11) =408408a(12) =668304a(13) =1058148a(14) =1627920a(15) =2441880a(16) =3581424a(17) =5148297a(18) =7268184a(19) =10094700a(20) =13813800a(21) =18648630a(22) =24864840a(23) =32776380a(24) =42751800a(25) =55221075a(26) =70682976a(27) =89713008a(28) =112971936a(29) =141214920