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%I #23 Apr 03 2023 10:36:13
%S 2,8,18,66,189,209,408,2208,2816,3168,3912,20909,54792,59973,157169,
%T 303093,709968,801978,1832496,2145353,2291610,5082306,10829346,
%U 16408818
%N Numbers k such that 3*2^k + 1 is a prime factor of a generalized Fermat number 5^(2^m) + 1 for some m.
%D Wilfrid Keller, private communication, 2008.
%H Anders Björn and Hans Riesel, <a href="http://dx.doi.org/10.1090/S0025-5718-98-00891-6">Factors of generalized Fermat numbers</a>, Math. Comp. 67 (1998), no. 221, pp. 441-446.
%H Anders Björn and Hans Riesel, <a href="http://dx.doi.org/10.1090/S0025-5718-05-01816-8">Table errata to “Factors of generalized Fermat numbers”</a>, Math. Comp. 74 (2005), no. 252, p. 2099.
%H Anders Björn and Hans Riesel, <a href="http://dx.doi.org/10.1090/S0025-5718-10-02371-9">Table errata 2 to "Factors of generalized Fermat numbers"</a>, Math. Comp. 80 (2011), pp. 1865-1866.
%H C. K. Caldwell, Top Twenty page, <a href="https://t5k.org/top20/page.php?id=29">Generalized Fermat Divisors (base=5)</a>
%H OEIS Wiki, <a href="/wiki/Generalized_Fermat_numbers">Generalized Fermat numbers</a>
%o (PARI) for(k=1,+oo,p=3*2^k+1;if(ispseudoprime(p),t=znorder(Mod(5,p));bitand(t,t-1)==0&&print1(k,", "))) \\ _Jeppe Stig Nielsen_, Oct 30 2020
%Y Cf. A199591, A268657, A204620, A268659, A268660, A268661, A268662, A268663, A226366, A268664. Subsequence of A002253.
%K nonn,hard
%O 1,1
%A _Arkadiusz Wesolowski_, Feb 10 2016
%E a(24) from _Jeppe Stig Nielsen_, Oct 30 2020
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