This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A121999 #17 Feb 16 2025 08:33:02
%S A121999 29,37,3373
%N A121999 Primes p such that p^2 divides Sierpinski number A014566((p-1)/2).
%C A121999 Subsequence of A003628.
%C A121999 No other terms below 10^11. - _Max Alekseyev_, Sep 18 2010
%H A121999 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/SierpinskiNumberoftheFirstKind.html">Sierpinski Number of the First Kind</a>.
%F A121999 Elements of A125854 that are congruent to 5 or 7 modulo 8, i.e., primes p such that p == 5 or 7 (mod 8) and 2^(p-1) == 1+p (mod p^2). - _Max Alekseyev_, Sep 18 2010
%t A121999 Do[p=Prime[n];f=((p-1)/2)^((p-1)/2)+1;If[IntegerQ[f/p^2],Print[p]],{n,1,3373}]
%o A121999 (PARI) { forprime(p=3, 10^11, if(Mod((p-1)/2, p^2)^((p-1)/2)==-1, print(p); )) } \\ _Max Alekseyev_, Sep 18 2010
%Y A121999 Cf. A014566, A003628.
%K A121999 bref,more,nonn
%O A121999 1,1
%A A121999 _Alexander Adamchuk_, Sep 11 2006