This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A137666 #22 Jul 26 2025 08:04:26
%S A137666 2,7,311,337,266981089,29914249171,7563707819165039903,192696104561,
%T A137666 58769065453824529,847499019384726257346113954958447091,
%U A137666 18158209813151,138233050898929517126243814850350442620694127
%N A137666 Largest prime factor of A137664(n) = (p + 1)^p - 1 for p = prime(n).
%C A137666 a(n) is also the largest prime factor of A137665(n) = A137664(n)/prime(n)^2. p^2 divides A137664(n) = (p + 1)^p - 1, p = prime(n). Least prime factors of A137664(n) are listed in A128456.
%C A137666 a(n) = A128456(n) = A137665(n) = ((p + 1)^p - 1)/p^2 for n = {1,2,3,7,595,...} corresponding to p = prime(n) = {2,3,5,17,4357,...} = A127837.
%H A137666 Amiram Eldar, <a href="/A137666/b137666.txt">Table of n, a(n) for n = 1..31</a> (terms 1..26 from Jens Kruse Andersen)
%t A137666 FactorInteger[#][[-1,1]]&/@((#+1)^#-1&/@Prime[Range[12]]) (* _Harvey P. Dale_, Apr 07 2018 *)
%Y A137666 Cf. A128452, A128456, A128356, A128357, A137664, A137665, A128466, A127837.
%K A137666 hard,nonn
%O A137666 1,1
%A A137666 _Alexander Adamchuk_, Feb 04 2008