A109602 - OEIS

%I #6 Nov 01 2019 16:30:11

%S 1,4,5,6,7,8,9,19,20,29,31,97,113,181,286,419,485,670,1216

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

%C Next term, if it exists, is > 3000. - _Ray Chandler_, Aug 04 2005

%t f[n_] := n!/Fold[Times, 1, Range[PrimePi[n]]]*2^n + 1; Do[ If[ PrimeQ[ f[n]], Print[n]], {n, 1000}]

%Y Cf. A108894.

%K nonn

%O 1,2

%A _Robert G. Wilson v_, Jul 18 2005

%E a(19)=1216 from _Ray Chandler_, Aug 04 2005