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Primes of the form n!! + (n+1)!!.
1

%I #16 Sep 24 2024 17:37:57

%S 2,3,5,11,23

%N Primes of the form n!! + (n+1)!!.

%C These are all primes of the form n!! + (n+1)!! Corresponding values of n are 0, 1, 2, 3, 4. At n>4, n!! + (n+1)!! is always composite, cf. A118333.

%C Apparently also the set of primes p(n) such that p(n)^2 - 2^n is prime. - _Irina Gerasimova_, May 09 2013

%t Select[Array[#!! + (# + 1)!! &, 12, 0], PrimeQ] (* _James C. McMahon_, Sep 24 2024 *)

%Y Cf. A118333.

%K fini,full,nonn

%O 1,1

%A _Zak Seidov_, Apr 23 2006