A123910 - OEIS

%I #19 Aug 30 2021 04:05:40

%S 5,7,9,11,13,15,19,25,35,79,81,105,171,243,271,295,355,523,591,1211,

%T 3073,11157,12887,19825

%N Numbers k such that k!!-4 is prime.

%C Corresponding primes of the form k!!-4 = a(n)!!-4 are {11, 101, 941, 10391, 135131, 2027021, 654729071, 7905853580621, 221643095476699771871, ...}.

%C a(25) > 50000. - _Robert Price_, May 08 2015

%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>

%t Do[f=n!!-4;If[PrimeQ[f],Print[{n,f}]],{n,1,355}]

%Y Cf. A007749, A094144.

%K hard,more,nonn

%O 1,1

%A _Alexander Adamchuk_, Oct 28 2006

%E More terms from _Farideh Firoozbakht_, Nov 19 2006

%E More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 03 2008

%E a(23)-a(24) from _Robert Price_, May 08 2015