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Numbers k such that (k!-8)/8 is prime.
3

%I #11 Oct 08 2016 12:32:12

%S 4,6,8,10,11,16,19,47,66,183,376,507,1081,1204,12111,23181

%N Numbers k such that (k!-8)/8 is prime.

%C a(17) > 25000. - _Robert Price_, Oct 08 2016

%p a:=proc(n) if isprime((1/8)*factorial(n)-1)=true then n else end if end proc: seq(a(n),n=4..550); # _Emeric Deutsch_, May 07 2008

%t a = {}; Do[If[PrimeQ[(n! - 8)/8], Print[a]; AppendTo[a, n]], {n, 1, 300}]; a

%Y Cf. A139189, A139190, A139191, A139192, A139193, A139194, A139195, A139196, A139197, A139198.

%Y Cf. n!/m-1 is a prime: A002982, A082671, A139056, A139199-A139205; n!/m+1 is a prime: A002981, A082672, A089085, A139061, A139058, A139063, A139065, A151913, A137390, A139071 (1<=m<=10).

%K hard,more,nonn

%O 1,1

%A _Artur Jasinski_, Apr 11 2008

%E 2 more terms from _Emeric Deutsch_, May 07 2008

%E More terms from _Serge Batalov_, Feb 18 2015

%E a(15)-a(16) from _Robert Price_, Oct 08 2016