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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 Table of n, a(n) for n=1..34. 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 Cf. A002981, A052747. Sequence in context: A359772 A158008 A106155 * A087190 A085038 A163078 Adjacent sequences: A271373 A271374 A271375 * A271377 A271378 A271379 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.)