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 A006514 M0653 #29 Jul 08 2025 16:48:43 %S A006514 2,3,5,7,11,13,17,19,23,31,37,41,59,61,67,83,89,97,101,103,107,109, %T A006514 127,131,137,139,149,167,197,199,227,241,269,271,281,293,347,373,379, %U A006514 421,457,487,521,523,607,727,809,881,971,983,997,1061,1063 %N A006514 Primes p such that 2^p - 1 has at most 2 prime factors. %C A006514 For a composite n, number 2^n - 1 has at most 2 prime factors only if n = p^2, where p is prime from the intersection of A000043 and A156585. The only known such primes are 2, 3, 7. - _Max Alekseyev_, Apr 23 2019 %C A006514 a(54) >= 1277. - _Max Alekseyev_, Apr 23 2019 %D A006514 J. Brillhart et al., Factorizations of b^n +- 1. Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 2nd edition, 1985; and later supplements. %D A006514 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A006514 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 A006514 S. S. Wagstaff, Jr., <a href="http://www.cerias.purdue.edu/homes/ssw/cun/index.html">The Cunningham Project</a> %t A006514 Select[Prime[Range[100]],PrimeOmega[2^#-1]<3&] (* _Harvey P. Dale_, Nov 11 2011 *) %Y A006514 Cf. A000043 (a subsequence), A001348, A088863. %K A006514 nonn %O A006514 1,1 %A A006514 _N. J. A. Sloane_ %E A006514 More terms from _Sean A. Irvine_, May 04 2017 %E A006514 Edited by _Max Alekseyev_, Apr 23 2019