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Numbers n such that (5+n!)/5 is prime.
26

%I #17 Sep 08 2022 08:45:33

%S 7,9,11,14,19,23,45,121,131,194,735,751,1316,1372,2084,2562,5678,5758,

%T 12533,24222

%N Numbers n such that (5+n!)/5 is prime.

%C For primes of the form (5+n!)/5 see A139059.

%C a(21) > 25000. - _Robert Price_, Nov 20 2016

%t a = {}; Do[If[PrimeQ[(n! + 5)/5], AppendTo[a, n]], {n, 1, 751}]; a

%o (Magma) [ n: n in [5..734] | IsPrime((Factorial(n)+5) div 5) ];

%o (PARI) A139058(n) = local(k=(n!+5)\5); if(isprime(k), k, 0);

%o for(n=5, 800, if(A139058(n)>0, print1(n, ", ")))

%Y Cf. A139059.

%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 nonn

%O 1,1

%A _Artur Jasinski_, Apr 07 2008

%E More terms from _Serge Batalov_, Feb 18 2015

%E a(19)-a(20) from _Robert Price_, Nov 20 2016