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Numbers n such that n!! - 2^n is prime.
3

%I #11 Sep 05 2015 03:08:52

%S 9,13,21,25,27,35,41,53,63,81,123,333,381,413,1187,2265,3153,4211,

%T 4887,7359,14161,14643,17299,22107,31487,40235,46711

%N Numbers n such that n!! - 2^n is prime.

%C All terms are odd.

%C a(28) > 50000. - _Robert Price_, Sep 04 2015

%e 9 is in the sequence because 9!! - 2^9 = 433 is prime.

%t Select[Range[0, 50000], #!! - 2^# > 0 && PrimeQ[#!! - 2^#] &] (* _Robert Price_, Sep 04 2015 *)

%Y Cf. A124248.

%K more,nonn

%O 1,1

%A _Farideh Firoozbakht_, Nov 27 2006

%E Three more terms from _Ryan Propper_, Nov 05 2007

%E a(21)-a(27) from _Robert Price_, Sep 04 2015