A273869 - OEIS

%I #31 Jun 05 2017 23:41:32

%S 3,11,14,53,110,216,322,364,389

%N Integers n such that floor(sqrt(n!)) (A055226(n)) is a prime number.

%C a(10) (if it exists) requires n > 4800.

%C No further terms <= 15000. - _Eric M. Schmidt_, Jun 05 2017

%e 3 is in the sequence because floor(sqrt(3!)) = 2 is prime.

%e 11 is in the sequence because floor(sqrt(11!)) = 6317 is prime.

%e 14 is in the sequence because floor(sqrt(14!)) = 295259 is prime.

%e 4 is not in the sequence because floor(sqrt(4!)) = 2^2.

%t Select[Table[n, {n, 1, 2500}], PrimeQ[Floor[Sqrt[#!]]] &]

%o (PARI) isok(n) = isprime(sqrtint(n!)); \\ _Michel Marcus_, Jun 10 2016

%o (PARI) lista(nn) = for(n=1, nn, if(ispseudoprime(sqrtint(n!)), print1(n, ", "))); \\ _Altug Alkan_, Jul 09 2016

%Y Cf. A055226.

%K nonn,more

%O 1,1

%A _Salvador Cerdá_, Jun 01 2016