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A271376 Integers n such that n!/(n-2) + 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 (list; graph; refs; listen; history; text; internal format)
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!/(n-2)+1), print1(n, ", ")));
(PFGW) ABC2 $a!/($a-2) + 1
a: from 3 to 100000
(Magma) [n: n in [3..500] | IsPrime(Factorial(n) div (n-2) + 1)]; // Vincenzo Librandi, Apr 07 2016
CROSSREFS
Sequence in context: A359772 A158008 A106155 * A087190 A085038 A163078
KEYWORD
nonn
AUTHOR
Altug Alkan, Apr 05 2016
EXTENSIONS
a(23) from Charles R Greathouse IV, Apr 05 2016
a(24)-a(27) from Charles R Greathouse IV, Apr 06 2016
a(28)-a(32) from Charles R Greathouse IV, Apr 18 2016
a(33) from Charles R Greathouse IV, Apr 30 2016
a(34) from Charles R Greathouse IV, May 09 2016
STATUS
approved

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Last modified February 22 10:17 EST 2024. Contains 370250 sequences. (Running on oeis4.)