A112855 - OEIS

%I #6 Nov 21 2013 12:48:45

%S 1,2,5,10,24,30,72,340,379,712,1020,1647,3654,7923

%N Numbers n such that (2*n)!/n!+1 is prime.

%C Next term is > 10000.

%t Select[Range[8000],PrimeQ[(2#)!/#!+1]&] (* _Harvey P. Dale_, Mar 23 2012 *)

%Y Cf. A112856 primes of the form (2*n)!/n!+1, A112853 (2*n)!/n!-1 is prime, A066726 (2*n)!/(n!)^2-1 is prime, A112859 (2*n)!/(n!)^2+1 is prime, A112861 (2*n)!/(2*(n!)^2)-1 is prime, A112863 (2*n)!/(2*(n!)^2)+1 is prime.

%K hard,nonn

%O 1,2

%A _Hugo Pfoertner_, Sep 25 2005