a(n) = n*(4*n^2+5*n-3)/2.

Terms

a(0) =3a(1) =23a(2) =72a(3) =162a(4) =305a(5) =513a(6) =798a(7) =1172a(8) =1647a(9) =2235a(10) =2948a(11) =3798a(12) =4797a(13) =5957a(14) =7290a(15) =8808a(16) =10523a(17) =12447a(18) =14592a(19) =16970a(20) =19593a(21) =22473a(22) =25622a(23) =29052a(24) =32775a(25) =36803a(26) =41148a(27) =45822a(28) =50837a(29) =56205