a(n) = 2*n! + 1.

Terms

a(0) =3a(1) =3a(2) =5a(3) =13a(4) =49a(5) =241a(6) =1441a(7) =10081a(8) =80641a(9) =725761a(10) =7257601a(11) =79833601a(12) =958003201a(13) =12454041601a(14) =174356582401