a(n) = (n+1)*binomial(n+1,6).

Terms

a(0) =6a(1) =49a(2) =224a(3) =756a(4) =2100a(5) =5082a(6) =11088a(7) =22308a(8) =42042a(9) =75075a(10) =128128a(11) =210392a(12) =334152a(13) =515508a(14) =775200a(15) =1139544a(16) =1641486a(17) =2321781a(18) =3230304a(19) =4427500a(20) =5985980a(21) =7992270a(22) =10548720a(23) =13775580a(24) =17813250a(25) =22824711a(26) =28998144a(27) =36549744a(28) =45726736a(29) =56810600