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 A291349 #8 Sep 25 2019 15:03:30 %S A291349 1,7,11,31,57,73,97,105,209,245,403,545,917,953,1177,1239,1283,1627, %T A291349 2465,3701,4479,4637,6349,7983,11155,13595,15547,17031,17609,24087, %U A291349 24707,39773,40407,63329 %N A291349 Numbers k such that k!4 + 2^8 is prime, where k!4 = k!!!! is the quadruple factorial number (A007662). %C A291349 Corresponding primes are: 257, 277, 487, 1267389841, ... %C A291349 a(35) > 10^5. %C A291349 Terms > 31 correspond to probable primes. %H A291349 Henri & Renaud Lifchitz, <a href="http://www.primenumbers.net/prptop/searchform.php?form=n%214%2B4&action=Search">PRP Records. Search for n!4+256.</a> %H A291349 Joe McLean, <a href="http://web.archive.org/web/20091027034731/http://uk.geocities.com/nassarawa%40btinternet.com/probprim2.htm">Interesting Sources of Probable Primes</a> %H A291349 OpenPFGW Project, <a href="http://sourceforge.net/projects/openpfgw/">Primality Tester</a> %e A291349 11!4 + 2^8 = 11*7*3*1 + 256 = 487 is prime, so 11 is in the sequence. %t A291349 MultiFactorial[n_, k_] := If[n < 1, 1, n*MultiFactorial[n - k, k]]; %t A291349 Select[Range[0, 50000], PrimeQ[MultiFactorial[#, 4] + 2^8] &] %Y A291349 Cf. A007662, A037082, A084438, A123910, A242994. %K A291349 nonn,more %O A291349 1,2 %A A291349 _Robert Price_, Aug 22 2017 %E A291349 a(34) from _Robert Price_, Sep 25 2019