A381258 Numbers k such that 7*k+1 divides 7^k+1.

0, 1, 135, 5733, 11229, 42705, 50445, 117649, 131365, 168093, 636405, 699825, 1269495, 2528155, 4226175, 6176709, 6502545, 9365265, 9551115, 13227021, 14464485, 14912625, 20859435, 26903605, 28251265, 30589905, 32660901, 37597329, 41506875, 42766465, 55452075, 56192535, 111898605

Offset: 1

Author

René-Louis Clerc, Feb 18 2025

Keywords

• nonn

Comments

The numbers are called Curzon numbers by Tattersall (p. 85, exercise 43).

References

• James J. Tattersall, Elementary Number Theory in Nine Chapters, Second Edition, Cambridge University Press, 2005, p. 85.

Links

• Giovanni Resta, Curzon numbers, Numbers Aplenty.

Crossrefs

Cf. A224486, A222948, A230076, A381256, A381257.

Programs

Mathematica

Select[Range[0,10^7],PowerMod[7,#,7#+1]==7#&] (* James C. McMahon, Mar 05 2025 *)

PARI

isok(n) = my(m=7*n+1); Mod(7, m)^n==-1