a(n) = floor(n*(n+2)*(2*n-1)/8).

Terms

a(0) =0a(1) =3a(2) =9a(3) =21a(4) =39a(5) =66a(6) =102a(7) =150a(8) =210a(9) =285a(10) =375a(11) =483a(12) =609a(13) =756a(14) =924a(15) =1116a(16) =1332a(17) =1575a(18) =1845a(19) =2145a(20) =2475a(21) =2838a(22) =3234a(23) =3666a(24) =4134a(25) =4641a(26) =5187a(27) =5775a(28) =6405a(29) =7080