a(n) = 25*n^3 - n*(5*n+1)/2 + 1.

Terms

a(0) =23a(1) =190a(2) =652a(3) =1559a(4) =3061a(5) =5308a(6) =8450a(7) =12637a(8) =18019a(9) =24746a(10) =32968a(11) =42835a(12) =54497a(13) =68104a(14) =83806a(15) =101753a(16) =122095a(17) =144982a(18) =170564a(19) =198991a(20) =230413a(21) =264980a(22) =302842a(23) =344149a(24) =389051a(25) =437698a(26) =490240a(27) =546827a(28) =607609a(29) =672736