A337829 - OEIS

%I #24 Oct 13 2020 15:43:20

%S 3,7,43,53,127,163,487,677,883,2647,8527,8803,14407,18523,26407,32887,

%T 35323,39367,71443,105967,184087,184843,230203,265483,319327,388963,

%U 425083,543607,554527,651043,688087,690607,698923,796447,887923,924043,1001323

%N Odd integers k such that 5^((k-1)/2) + 1 == 0 (mod k*(k-1)/2).

%C The first 564 terms are prime.

%H Chai Wah Wu, <a href="/A337829/b337829.txt">Table of n, a(n) for n = 1..564</a>

%t Select[Range[3, 10^6, 2], PowerMod[5, (# - 1)/2, (t = #*(# - 1)/2)] == t - 1 &] (* _Amiram Eldar_, Sep 24 2020 *)

%Y Cf. A337818.

%K nonn

%O 1,1

%A _Benoit Cloitre_, Sep 24 2020