A133378 - OEIS

A133378

a(1)=1. For n >= 2, a(n) = the largest prime divisor of (a(n-1)^a(n-1) + 1).

%I #21 Jan 28 2023 12:29:14

%S 1,2,5,521

%N a(1)=1. For n >= 2, a(n) = the largest prime divisor of (a(n-1)^a(n-1) + 1).

%C a(5) depends on the factorization of the 1408-digit composite number (521^521+1)/(2 * 3^2 * 29 * 375121); see factordb.com link. - _Michael S. Branicky_, Jan 27 2023

%H factordb.com, <a href="http://factordb.com/index.php?id=1100000000195192576">521^521+1</a>.

%t NestList[FactorInteger[#^#+1][[-1,1]]&,1,3] (* _Harvey P. Dale_, Jun 21 2012 *)

%Y Cf. A007571.

%K more,nonn

%O 1,2

%A _Leroy Quet_, Oct 28 2007