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 A289547 Numbers k such that k!6 - 4 is prime, where k!6 is the sextuple factorial number (A085158 ). 1

%I

%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&amp;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

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Last modified February 19 19:06 EST 2020. Contains 332047 sequences. (Running on oeis4.)