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 A076133 #35 Jun 06 2025 14:36:24 %S A076133 2,3,4,5,6,7,14,15,17,22,28,91,253,257,298,659,832,866,1849,2495,2716, %T A076133 2773,2831,3364,5264,7429,28539,32123,37868,65591,113920 %N A076133 Numbers k such that 2*k! - 1 is prime. %C A076133 a(32) > 116000. - _Serge Batalov_, Jun 06 2025 %e A076133 k = 5 is here because 2*5! - 1 = 239 is prime. %t A076133 Select[Range[8000], PrimeQ[2 #! - 1] &] (* _Vincenzo Librandi_, Feb 20 2015 *) %o A076133 (Magma) [n: n in [1..600] | IsPrime(2*Factorial(n)-1)]; // _Vincenzo Librandi_, Feb 20 2015 %o A076133 (PARI) is(k) = ispseudoprime(2*k!-1); \\ _Jinyuan Wang_, Feb 04 2020 %Y A076133 Cf. A051915. %Y A076133 Cf. A002982, A076134, A099350, A099351, A180627, A180628, A180629, A180630, A180631. %K A076133 nonn,more %O A076133 1,1 %A A076133 Phillip L. Poplin (plpoplin(AT)bellsouth.net), Oct 30 2002 %E A076133 a(24)-a(29) from _Serge Batalov_, Feb 18 2015 %E A076133 a(30) from _Serge Batalov_, Jun 03 2025 %E A076133 a(31) from _Serge Batalov_, Jun 06 2025