a(n) = largest prime factor of n^n - 1.

Terms

a(0) =3a(1) =13a(2) =17a(3) =71a(4) =43a(5) =4733a(6) =241a(7) =757a(8) =9091a(9) =1806113a(10) =20593a(11) =1803647a(12) =8108731a(13) =39225301a(14) =6700417a(15) =2699538733a(16) =465841a(18) =222361a(19) =227633407a(20) =285451051007a(22) =1134793633a(23) =50150933101a(24) =3574533119a(26) =1100860153