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

1,1

Comments

Computed terms are prime.

Links

Table of n, a(n) for n=1..12.

Mathematica

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

Crossrefs

Cf. A337818.

Sequence in context: A009765 A113073 A349045 * A337828 A275749 A057207

Adjacent sequences: A337828 A337829 A337830 * A337832 A337833 A337834

Keyword

nonn,more

Author

Benoit Cloitre, Sep 24 2020

Extensions

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

Status

approved