|
%I #15 Nov 29 2018 17:21:44
%S 6,7,9,15,21,27,29,321,327,333,567,1025,4263,4365,5175,5655,9221,9327,
%T 9681,19685,24777,57869,58737
%N Numbers k such that k!6 - 4 is prime, where k!6 is the sextuple factorial number (A085158 ).
%C Corresponding primes are: 2, 3, 23, 401, 8501, 229631, 623641, ...
%C a(24) > 10^5.
%C Terms > 29 correspond to probable primes.
%H Henri & Renaud Lifchitz, <a href="http://www.primenumbers.net/prptop/searchform.php?form=n!6-4&action=Search">PRP Records. Search for n!6-4.</a>
%H 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 OpenPFGW Project, <a href="http://sourceforge.net/projects/openpfgw/">Primality Tester</a>
%e 15!6 - 4 = 15*9*3 - 4 = 401 is prime, so 15 is in the sequence.
%t MultiFactorial[n_, k_] := If[n < 1, 1, n*MultiFactorial[n - k, k]];
%t Select[Range[4, 50000], PrimeQ[MultiFactorial[#, 6] - 4] &]
%Y Cf. A007661, A037082, A084438, A123910, A242994.
%K nonn,more
%O 1,1
%A _Robert Price_, Jul 07 2017
%E a(22)-a(23) from _Robert Price_, Aug 03 2018
|
