A033981 Integers k such that 2^k == 7 (mod k).

1, 5, 25, 1727, 3830879, 33554425, 19584403931, 25086500333, 23476467919565, 4463061944990945

Offset: 1

Author

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

Keywords

• nonn
• more

Comments

A larger term: 15237454403219419167053498809.

Programs

Mathematica

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

PARI

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

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