a(n) = n*(3*n^4 + 15*n^3 + 25*n^2 - 15*n - 28)/60.

Terms

a(0) =0a(1) =0a(2) =7a(3) =40a(4) =136a(5) =356a(6) =791a(7) =1568a(8) =2856a(9) =4872a(10) =7887a(11) =12232a(12) =18304a(13) =26572a(14) =37583a(15) =51968a(16) =70448a(17) =93840a(18) =123063a(19) =159144a(20) =203224a(21) =256564a(22) =320551a(23) =396704a(24) =486680a(25) =592280a(26) =715455a(27) =858312a(28) =1023120a(29) =1212316