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 A375236 #8 Feb 16 2025 08:34:07 %S A375236 2,3,353,751,9587 %N A375236 Numbers k such that (21^k - 2^k)/19 is prime. %C A375236 The definition implies that k must be a prime. %C A375236 a(6) > 10^5. %H A375236 P. Bourdelais, <a href="https://listserv.nodak.edu/cgi-bin/wa.exe?A2=NMBRTHRY;417ab0d6.0906">A Generalized Repunit Conjecture</a>. %H A375236 J. Brillhart et al., <a href="http://dx.doi.org/10.1090/conm/022">Factorizations of b^n +- 1</a>, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002. %H A375236 H. Dubner and T. Granlund, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL3/DUBNER/dubner.html">Primes of the Form (b^n+1)/(b+1)</a>, J. Integer Sequences, 3 (2000), #P00.2.7. %H A375236 H. Lifchitz, <a href="http://www.primenumbers.net/Henri/us/MersFermus.htm">Mersenne and Fermat primes field</a> %H A375236 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Repunit.html">Repunit</a>. %t A375236 Select[Prime[Range[100]], PrimeQ[(21^# - 2^#)/19] &] %Y A375236 Cf. A062587, A062589, A127996, A127997, A128344, A204940, A217320, A225807, A229542, A375161. %K A375236 nonn,hard,more %O A375236 1,1 %A A375236 _Robert Price_, Aug 06 2024