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 A283191 #17 Jan 30 2025 14:43:31 %S A283191 7,13,19,31,373,811,1117,5059,12601 %N A283191 Prime numbers p such that (2^p - 5)/3 is prime. %C A283191 Let W = (2^p - 5)/3 and s = (W+1)/(2*p), then 5^s == 2 (mod W) for terms 1..9. %C A283191 Subsequence of 7, 13, 19, 31, 51, 55, 85, 111, 319, 373,.. which are numbers m such that (2^m-5)/3 is prime. - _R. J. Mathar_, Mar 05 2017 %C A283191 a(10) > 3*10^5. - _Michael S. Branicky_, Jan 30 2025 %t A283191 Select[Prime@ Range[2, 1000], PrimeQ[(2^# - 5)/3] &] (* _Michael De Vlieger_, Mar 03 2017 *) %o A283191 (PARI) %o A283191 forprime(p=3, 30000, W= (2^p-5)/3; if(ispseudoprime(W), print1(p, ", "))) %Y A283191 Cf. A000978. %K A283191 nonn,more %O A283191 1,1 %A A283191 _Dmitry Ezhov_, Mar 02 2017