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URL: https://oeis.org/A033981

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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
OFFSET
1,2
COMMENTS
A larger term: 15237454403219419167053498809.
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
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