%I #18 Feb 10 2019 18:58:10

%S 2,2,3,11,19,31,79,211,607,1931,6337,21961,78919,295291,1143563,

%T 4574149,18859777,80014843,348776611,1559776279,7147792903,

%U 33526120129,160785623729,787685471519,3938427356629,20082117944579,104349745809137,552166953567737

%N a(n) is the smallest prime x such that x^2-n! is also prime.

%C Every prime > 3 in this sequence is bigger than the n-th prime, see comment to A121926. For the smallest number x such that x^2-n! is prime see A143931. For the smallest prime numbers of the form x^2-n! see A143932.

%H Robert Israel, <a href="/A143933/b143933.txt">Table of n, a(n) for n = 1..300</a>

%p f:= proc(n) local p,t;

%p t:= n!;

%p p:= floor(sqrt(t));

%p do

%p p:= nextprime(p);

%p if isprime(p^2-t) then return p fi

%p od

%p end proc:

%p map(f, [$1..28]); # _Robert Israel_, Feb 10 2019

%t f[n_] := Block[{p = NextPrime[ Sqrt[ n!]]}, While[ !PrimeQ[p^2 - n!], p = NextPrime@ p]; p]; Array[f, 27] (* _Robert G. Wilson v_, Jan 08 2015 *)

%o (PARI) a(n)=my(N=n!,x=sqrtint(N)+1); while(!isprime(x^2-N), x=nextprime(x+1)); x \\ _Charles R Greathouse IV_, Dec 09 2014

%Y Cf. A121926, A143931, A143932.

%K nonn

%O 1,1

%A _Artur Jasinski_, Sep 05 2008

%E Corrected by _Charles R Greathouse IV_, Dec 09 2014