a(n) = n*(n+1)*(6*n-5)/2.

Terms

a(0) =0a(1) =1a(2) =21a(3) =78a(4) =190a(5) =375a(6) =651a(7) =1036a(8) =1548a(9) =2205a(10) =3025a(11) =4026a(12) =5226a(13) =6643a(14) =8295a(15) =10200a(16) =12376a(17) =14841a(18) =17613a(19) =20710a(20) =24150a(21) =27951a(22) =32131a(23) =36708a(24) =41700a(25) =47125a(26) =53001a(27) =59346a(28) =66178a(29) =73515