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 A256594 Numbers k such that k!*2^k + 1 is prime. 1
 0, 1, 259, 16708, 18655, 26304, 61999, 110251 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS FORMULA a(n) = A080778(n+1)/2 for n >= 2. - Amiram Eldar, Dec 06 2018 EXAMPLE 0 is in the sequence since 0!*2^0 + 1 = 2 is prime. MATHEMATICA Select[Range[0, 20000], PrimeQ[2^#*#! + 1] &] PROG (MAGMA) [n: n in [0..3*10^2] | IsPrime(Factorial(n)*2^n+1)]; // Vincenzo Librandi, Apr 05 2015 (PARI) for(n=0, 300, if(ispseudoprime(n!*2^n+1), print1(n, ", "))) \\ Derek Orr, Apr 05 2015 (Python) from sympy import factorial, isprime for n in range(0, 300):     if isprime(factorial(n)*(2**n)+1):         print(n, end=', ') # Stefano Spezia, Dec 06 2018 CROSSREFS Cf. A007749, A080778, A117141, A091415. Sequence in context: A038480 A254642 A322882 * A229433 A022221 A121918 Adjacent sequences:  A256591 A256592 A256593 * A256595 A256596 A256597 KEYWORD nonn,hard,more AUTHOR Robert Price, Apr 03 2015 EXTENSIONS a(6)-a(8), from the data at A080778, added by Amiram Eldar, Dec 06 2018 STATUS approved

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Last modified April 26 08:03 EDT 2019. Contains 322472 sequences. (Running on oeis4.)