A239412 Numbers n such that (n!-k)/(n-k) is prime for some k.
4, 6, 8, 16, 18, 92, 254, 258, 660, 1850, 2496, 2774, 2832, 7430, 28540, 32124
Offset: 1
Examples
(4!-k)/(4-k) is prime for some k (namely, k = 2). Thus, 4 is a member of this sequence.
Crossrefs
Cf. A076133.
Programs
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Maple
select(t -> isprime(2*(t-1)!-1), [seq(q,q=2..1000, 2)]); # Robert Israel, Aug 11 2016
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Mathematica
Select[Range[2, 10^3, 2], PrimeQ[2 (# - 1)! - 1] &] (* Michael De Vlieger, Aug 11 2016 *)
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PARI
a(n)=for(k=1,int(n/2),s=(n!-k)/(n-k);if(floor(s)==s,if(ispseudoprime(s),return(k)))) n=1;while(n<1000,if(a(n),print1(n,", "));n+=1)
Extensions
Edited and a(14)-a(16) added by Robert Israel, Aug 11 2016
Comments