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

Terms

a(0) =1a(1) =1a(2) =4a(3) =13a(4) =31a(5) =61a(6) =106a(7) =169a(8) =253a(9) =361a(10) =496a(11) =661a(12) =859a(13) =1093a(14) =1366a(15) =1681a(16) =2041a(17) =2449a(18) =2908a(19) =3421a(20) =3991a(21) =4621a(22) =5314a(23) =6073a(24) =6901a(25) =7801a(26) =8776a(27) =9829a(28) =10963a(29) =12181