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%I #13 Feb 17 2014 06:12:51
%S 3628679,87178286159,20922789847679,265252859812191058635000805631999
%N Primes of the form (2n)! - n! - 1.
%C The term a(7) (2407 digits) is too large to include even in the b-file.
%C All the numbers end in 9.
%C For all n, (2n)! - n! - 1 has exactly A027868(n) trailing 9s. - _Rick L. Shepherd_, Feb 16 2014
%C Generated by n = 5, 7, 8, 15, 103, 179, .... - _R. J. Mathar_, Sep 20 2012 (now A238011)
%D G. Balzarotti and P. P. Lava, Le sequenze di numeri interi, Hoepli, 2008, p. 159.
%H Rick L. Shepherd, <a href="/A118813/b118813.txt">Table of n, a(n) for n = 1..6</a>
%e For n=5, (2*5)! - 5! - 1 = 3628800 - 120 - 1 = 3628679, which is prime.
%p PFACT:=proc(N) local i,r; for i from 1 by 1 to N do r:=(2*i)!-i!-1; if isprime(r) then print(i); fi; od; end: PFACT(100);
%Y Cf. A238011 (corresponding n), A118812, A237443.
%K nonn
%O 1,1
%A _Paolo P. Lava_ and _Giorgio Balzarotti_, May 23 2006