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A257864 Numbers n such that n!! - 2^7 is prime. 2
11, 13, 21, 47, 59, 77, 109, 129, 155, 163, 245, 337, 511, 1417, 3013, 3757, 4989, 8977, 12479, 12869 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(21) > 50000. - Robert Price, May 11 2015

a(n) is odd. - Chai Wah Wu, May 12 2015

LINKS

Table of n, a(n) for n=1..20.

C. K. Caldwell, The Prime Glossary, multifactorial prime

Joe McLean, Interesting Sources of Probable Primes

MATHEMATICA

Select[Range[0, 50000], #!! - 128 > 0 && PrimeQ[#!! - 128] &]

PROG

(PARI) is(n)=ispseudoprime(prod(i=0, (n-1)\2, n-2*i)-128) \\ Charles R Greathouse IV, May 11 2015

(Python)

from gmpy2 import is_prime, mpz

A257864_list, g, h = [], mpz(105), mpz(128)

for i in range(9, 10**5, 2):

....g *= i

....if is_prime(g-h):

........A257864_list.append(i) # Chai Wah Wu, May 12 2015

(Perl)

use ntheory ":all"; use Math::GMPz;

sub mf2 { my($n, $P)=(shift, Math::GMPz->new(1)); $P *= $n-($_<<1) for 0..($n-1)>>1; $P; }

for (1..100000) { say if is_prob_prime(mf2($_)-128) } # Dana Jacobsen, May 13 2015

CROSSREFS

Cf. A007749, A094144, A123910  (other forms of n!!-2^k)

Cf. A080778, A076185, A076186, A076188, A076189, A076190, A076193, A076194, A076195, A076196, A076197  (other forms of n!!+2^k)

Sequence in context: A102907 A235479 A089774 * A248599 A274243 A192931

Adjacent sequences:  A257861 A257862 A257863 * A257865 A257866 A257867

KEYWORD

nonn,hard,more

AUTHOR

Robert Price, May 11 2015

STATUS

approved

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Last modified April 18 12:42 EDT 2019. Contains 322209 sequences. (Running on oeis4.)