a(n) = n*(n+1)*(2*n^2+1)/6.

Terms

a(0) =0a(1) =1a(2) =9a(3) =38a(4) =110a(5) =255a(6) =511a(7) =924a(8) =1548a(9) =2445a(10) =3685a(11) =5346a(12) =7514a(13) =10283a(14) =13755a(15) =18040a(16) =23256a(17) =29529a(18) =36993a(19) =45790a(20) =56070a(21) =67991a(22) =81719a(23) =97428a(24) =115300a(25) =135525a(26) =158301a(27) =183834a(28) =212338a(29) =244035