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 A209271 #18 Apr 15 2025 09:40:49
%S A209271 5,13,181,613,761,1201,8581,9661,21013,26681,34061,59513,68821,101701,
%T A209271 156241,584281,637321,718801,782501,787513,1078981,1193513,1336613,
%U A209271 1470613,1529501,1639861,1757813,2103301,2257813,2287661,2601481,3540461,4307113
%N A209271 Primes p such that A066272(p)*p+1 is also prime, where A066272 is the number of anti-divisors.
%C A209271 Could be called "Sophie Germain anti-primes" or "anti-Sophie Germain primes". Inspired by the Gerasimov link.
%C A209271 Sophie Germain primes are such that 2p+1 is also prime, where 2 is the number of divisors of p. Here this is replaced with the number of anti-divisors.
%C A209271 There are only 47 such primes below 10^7.
%H A209271 Donovan Johnson, <a href="/A209271/b209271.txt">Table of n, a(n) for n = 1..1000</a>
%H A209271 J. S. Gerasimov, <a href="https://web.archive.org/web/20201230073136/http://list.seqfan.eu/pipermail/seqfan/2013-January/010687.html">Sophie Germain nonprimes</a> [title corrected], SeqFan mailing list, Jan 15 2013
%o A209271 (PARI) {forprime(n=1,default(primelimit),isprime(A066272(n)*n+1) & print1(n","))}
%Y A209271 Cf. A066272.
%K A209271 nonn
%O A209271 1,1
%A A209271 _M. F. Hasler_, Jan 15 2013