a(n) = ((3*n + 1)^6 - 1)/9.

Terms

a(0) =0a(1) =455a(2) =13072a(3) =111111a(4) =536312a(5) =1864135a(6) =5227320a(7) =12597767a(8) =27126736a(9) =53543367a(10) =98611520a(11) =171644935a(12) =285080712a(13) =455111111a(14) =702373672a(15) =1052699655a(16) =1537920800a(17) =2196734407a(18) =3075626736a(19) =4229854727a(20) =5724486040a(21) =7635497415a(22) =10050931352a(23) =13072111111a(24) =16814914032a(25) =21411103175a(26) =27009717280