a(n) = 4*n! + 1.

Terms

a(0) =5a(1) =5a(2) =9a(3) =25a(4) =97a(5) =481a(6) =2881a(7) =20161a(8) =161281a(9) =1451521a(10) =14515201a(11) =159667201a(12) =1916006401a(13) =24908083201a(14) =348713164801