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A033981 Integers k such that 2^k == 7 (mod k). 19
1, 5, 25, 1727, 3830879, 33554425, 19584403931, 25086500333, 23476467919565, 4463061944990945 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

A larger term: 15237454403219419167053498809.

LINKS

Table of n, a(n) for n=1..10.

MATHEMATICA

m = 7; Join[Select[Range[m], Divisible[2^# - m, #] &],

Select[Range[m + 1, 10^7], PowerMod[2, #, #] == m &]] (* Robert Price, Sep 26 2018 *)

PROG

(PARI) isok(n) = Mod(2, n)^n == 7; \\ Michel Marcus, Sep 27 2018

CROSSREFS

Sequence in context: A278120 A039780 A328124 * A099077 A137113 A137115

Adjacent sequences:  A033978 A033979 A033980 * A033982 A033983 A033984

KEYWORD

nonn,more

AUTHOR

Joe K. Crump (joecr(AT)carolina.rr.com)

EXTENSIONS

Terms 1, 5 prepended by Max Alekseyev, May 18 2011

a(9) added by Max Alekseyev, May 21 2011

a(10) from Max Alekseyev, Jun 17 2012

STATUS

approved

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Last modified August 11 07:13 EDT 2022. Contains 356046 sequences. (Running on oeis4.)