a(n) = (6*n + 1)^4.

Terms

a(0) =1a(1) =2401a(2) =28561a(3) =130321a(4) =390625a(5) =923521a(6) =1874161a(7) =3418801a(8) =5764801a(9) =9150625a(10) =13845841a(11) =20151121a(12) =28398241a(13) =38950081a(14) =52200625a(15) =68574961a(16) =88529281a(17) =112550881a(18) =141158161a(19) =174900625a(20) =214358881a(21) =260144641a(22) =312900721a(23) =373301041a(24) =442050625a(25) =519885601a(26) =607573201a(27) =705911761