a(n) = n*(n+1)*(7*n-6)/2.

Terms

a(0) =0a(1) =1a(2) =24a(3) =90a(4) =220a(5) =435a(6) =756a(7) =1204a(8) =1800a(9) =2565a(10) =3520a(11) =4686a(12) =6084a(13) =7735a(14) =9660a(15) =11880a(16) =14416a(17) =17289a(18) =20520a(19) =24130a(20) =28140a(21) =32571a(22) =37444a(23) =42780a(24) =48600a(25) =54925a(26) =61776a(27) =69174a(28) =77140a(29) =85695