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A268658 Numbers k such that 3*2^k + 1 is a prime factor of a generalized Fermat number 5^(2^m) + 1 for some m. 10
2, 8, 18, 66, 189, 209, 408, 2208, 2816, 3168, 3912, 20909, 54792, 59973, 157169, 303093, 709968, 801978, 1832496, 2145353, 2291610, 5082306, 10829346, 16408818 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

REFERENCES

Wilfrid Keller, private communication, 2008.

LINKS

Table of n, a(n) for n=1..24.

Anders Björn and Hans Riesel, Factors of generalized Fermat numbers, Math. Comp. 67 (1998), no. 221, pp. 441-446.

Anders Björn and Hans Riesel, Table errata to “Factors of generalized Fermat numbers”, Math. Comp. 74 (2005), no. 252, p. 2099.

Anders Björn and Hans Riesel, Table errata 2 to "Factors of generalized Fermat numbers", Math. Comp. 80 (2011), pp. 1865-1866.

C. K. Caldwell, Top Twenty page, Generalized Fermat Divisors (base=5)

OEIS Wiki, Generalized Fermat numbers

PROG

(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

CROSSREFS

Cf. A199591, A268657, A204620, A268659, A268660, A268661, A268662, A268663, A226366, A268664. Subsequence of A002253.

Sequence in context: A058082 A005675 A054358 * A074128 A061226 A134827

Adjacent sequences:  A268655 A268656 A268657 * A268659 A268660 A268661

KEYWORD

nonn,hard

AUTHOR

Arkadiusz Wesolowski, Feb 10 2016

EXTENSIONS

a(24) from Jeppe Stig Nielsen, Oct 30 2020

STATUS

approved

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Last modified October 15 21:38 EDT 2021. Contains 348034 sequences. (Running on oeis4.)