A337831 Odd integers k such that 7^((k-1)/2) + 1 == 0 (mod k*(k-1)/2).

5, 101, 62501, 1020101, 3512501, 12650501, 22598021, 31562501, 365328101, 789062501, 11412000101, 64014060101

Offset: 1

Author

Benoit Cloitre, Sep 24 2020

Keywords

• nonn
• more

Comments

Computed terms are prime.

Crossrefs

Cf. A337818.

Programs

Mathematica

Select[Range[3, 10^7, 2], PowerMod[7, (# - 1)/2, (t = #*(# - 1)/2)] == t - 1 &] (* Amiram Eldar, Sep 24 2020 *)

Extensions

a(9)-a(12) from Amiram Eldar, Sep 25 2020