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

Terms

a(0) =0a(1) =1a(2) =11a(3) =39a(4) =94a(5) =185a(6) =321a(7) =511a(8) =764a(9) =1089a(10) =1495a(11) =1991a(12) =2586a(13) =3289a(14) =4109a(15) =5055a(16) =6136a(17) =7361a(18) =8739a(19) =10279a(20) =11990a(21) =13881a(22) =15961a(23) =18239a(24) =20724a(25) =23425a(26) =26351a(27) =29511a(28) =32914a(29) =36569