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a(n) is the greatest prime factor of a(n-1)^2+a(n-1)+1.
7

%I #7 May 10 2013 12:44:31

%S 2,7,19,127,5419,1009,9181,1423,96493,163350799,25249969,

%T 212520319916977,784949209969,145542538757017,147660435988297,

%U 2508855873622663,3565137918692593,6521735641,11273204227,16141059763,125679599753438821,240780337980146570229319,7282590063606707136764017

%N a(n) is the greatest prime factor of a(n-1)^2+a(n-1)+1.

%C Except for the first term the initial (ten at least) terms are one more than a multiple of 6, with the result that a(n)^2+a(n)+1 is in these cases an odd multiple of 3 and appears to be 3 times the product of primes all of which are one more than a multiple of 6.

%H Dennis Langdeau, <a href="/A056650/b056650.txt">Table of n, a(n) for n = 0..31</a>

%Y Cf. A031439, A045375.

%K nonn

%O 0,1

%A _Henry Bottomley_, Aug 09 2000

%E More terms from _Vladeta Jovovic_, Nov 26 2001