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

Terms

a(0) =81a(1) =2401a(2) =14641a(3) =50625a(4) =130321a(5) =279841a(6) =531441a(7) =923521a(8) =1500625a(9) =2313441a(10) =3418801a(11) =4879681a(12) =6765201a(13) =9150625a(14) =12117361a(15) =15752961a(16) =20151121a(17) =25411681a(18) =31640625a(19) =38950081a(20) =47458321a(21) =57289761