A257864 Numbers n such that n!! - 2^7 is prime.

11, 13, 21, 47, 59, 77, 109, 129, 155, 163, 245, 337, 511, 1417, 3013, 3757, 4989, 8977, 12479, 12869

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: A346287 A330975 A351841 * A248599 A366379 A274243

Adjacent sequences: A257861 A257862 A257863 * A257865 A257866 A257867

Keyword

nonn,hard,more

Author

Robert Price, May 11 2015

Status

approved