a(n) = largest prime of the form n!/k! + 1.

Terms

a(0) =2a(1) =2a(2) =3a(3) =7a(4) =13a(5) =61a(6) =31a(7) =2521a(8) =20161a(9) =15121a(10) =604801a(11) =39916801a(12) =3991681a(13) =3113510401a(14) =14529715201a(15) =54486432001a(19) =2a(20) =670442572801