a(n) = (n^7 - n)/42.

Terms

a(0) =0a(1) =0a(2) =3a(3) =52a(4) =390a(5) =1860a(6) =6665a(7) =19608a(8) =49932a(9) =113880a(10) =238095a(11) =463980a(12) =853138a(13) =1494012a(14) =2509845a(15) =4068080a(16) =6391320a(17) =9769968a(18) =14576667a(19) =21282660a(20) =30476190a(21) =42883060a(22) =59389473a(23) =81067272a(24) =109201700a(25) =145321800a(26) =191233575a(27) =249056028a(28) =321260202a(29) =410711340