

A271376


Integers n such that n!/(n2) + 1 is prime.


1



3, 4, 5, 6, 7, 10, 12, 13, 21, 24, 37, 64, 68, 136, 169, 216, 276, 435, 617, 753, 1722, 1775, 2762, 3974, 5006, 5931, 7480, 11442, 11896, 13200, 13534, 23240, 27971, 31867
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OFFSET

1,1


COMMENTS

Corresponding primes are 7, 13, 41, 181, 1009, 453601, ...


LINKS



EXAMPLE

3 is a term because 2*3 + 1 = 7 is prime.
4 is a term because 1*3*4 + 1 = 13 is prime.
5 is a term because 1*2*4*5 + 1 = 41 is prime.
6 is a term because 1*2*3*5*6 + 1 = 181 is prime.
7 is a term because 1*2*3*4*6*7 + 1 = 1009 is prime.


MATHEMATICA

Select[Range[3, 2000], PrimeQ[( #! / (#  2) + 1)] &] (* Vincenzo Librandi, Apr 07 2016 *)


PROG

(PARI) lista(nn) = for(n=3, nn, if(ispseudoprime(n!/(n2)+1), print1(n, ", ")));
(PFGW) ABC2 $a!/($a2) + 1
a: from 3 to 100000
(Magma) [n: n in [3..500]  IsPrime(Factorial(n) div (n2) + 1)]; // Vincenzo Librandi, Apr 07 2016


CROSSREFS



KEYWORD

nonn


AUTHOR



EXTENSIONS



STATUS

approved



