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 A385680 #6 Aug 10 2025 22:06:04 %S A385680 2,5,1549,4391 %N A385680 Numbers k such that (40^k - 3^k)/37 is prime. %C A385680 The definition implies that k must be a prime. %C A385680 a(5) > 10^5. %H A385680 P. Bourdelais, <a href="https://listserv.nodak.edu/cgi-bin/wa.exe?A2=NMBRTHRY;417ab0d6.0906">A Generalized Repunit Conjecture</a>. %H A385680 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 A385680 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 A385680 H. Lifchitz, <a href="http://www.primenumbers.net/Henri/us/MersFermus.htm">Mersenne and Fermat primes field</a> %H A385680 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Repunit.html">Repunit</a>. %H A385680 OEIS Wiki, <a href="https://oeis.org/wiki/Primes_of_the_form_(a%5En%2Bb%5En)/(a%2Bb)_and_(a%5En-b%5En)/(a-b)">Primes of the form (a^n+b^n)/(a+b) and (a^n-b^n)/(a-b)</a> %t A385680 Select[Prime[Range[10000]], PrimeQ[(40^# - 3^#)/37] &] %Y A385680 Cf. A062587, A062589, A127996, A127997, A128344, A204940, A217320, A225807, A229542, A375161, A375236, A377031. %K A385680 nonn,hard,more %O A385680 1,1 %A A385680 _Robert Price_, Aug 04 2025