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%I #17 May 31 2024 19:57:08
%S 3,4,6,8,12,16,22,24,54,56,98,152,156,176,256,454,460,720,750,770,800,
%T 1442,2846,5920,7066,12778,19978,22726,25938,27780,36072,39746,48244
%N Numbers k such that k!!!! - 1 is prime.
%C The search for multifactorial primes started by Ray Ballinger is now continued by a team of volunteers on the website of Ken Davis (see link).
%H Ken Davis, <a href="http://mfprimes.free-dc.org">Status of Search for Multifactorial Primes</a>.
%H Ken Davis, <a href="http://mfprimes.free-dc.org/mfdata/f04m.html">Results for n!4-1</a>.
%t MultiFactorial[n_, k_] := If[n < 1, 1, n*MultiFactorial[n - k, k]];
%t Select[Range[0, 1000], PrimeQ[MultiFactorial[#, 4] - 1] & ] (* _Robert Price_, Apr 19 2019 *)
%t Select[Range[48300],PrimeQ[Times@@Range[#,1,-4]-1]&] (* _Harvey P. Dale_, Aug 11 2020 *)
%Y Cf. A007662 (quadruple factorials), A085146.
%K hard,nonn
%O 1,1
%A _Hugo Pfoertner_, Jun 25 2003
%E More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 03 2008