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

Terms

a(0) =1a(1) =6a(2) =20a(3) =49a(4) =99a(5) =176a(6) =286a(7) =435a(8) =629a(9) =874a(10) =1176a(11) =1541a(12) =1975a(13) =2484a(14) =3074a(15) =3751a(16) =4521a(17) =5390a(18) =6364a(19) =7449a(20) =8651a(21) =9976a(22) =11430a(23) =13019a(24) =14749a(25) =16626a(26) =18656a(27) =20845a(28) =23199a(29) =25724