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

Terms

a(0) =1a(1) =1a(2) =6a(3) =22a(4) =55a(5) =111a(6) =196a(7) =316a(8) =477a(9) =685a(10) =946a(11) =1266a(12) =1651a(13) =2107a(14) =2640a(15) =3256a(16) =3961a(17) =4761a(18) =5662a(19) =6670a(20) =7791a(21) =9031a(22) =10396a(23) =11892a(24) =13525a(25) =15301a(26) =17226a(27) =19306a(28) =21547a(29) =23955