a(n) = (n^3 + 3*n^7)/4.

Terms

a(0) =1a(1) =98a(2) =1647a(3) =12304a(4) =58625a(5) =210006a(6) =617743a(7) =1572992a(8) =3587409a(9) =7500250a(10) =14615711a(11) =26874288a(12) =47061937a(13) =79060814a(14) =128145375a(15) =201327616a(16) =307755233a(17) =459166482a(18) =670405519a(19) =960002000a(20) =1350818721a(21) =1870771078a(22) =2553622127a(23) =3439857024a(24) =4577640625a(25) =6023862026a(26) =7845269823