A057202 Numbers n such that 2^n - 21 is prime.

1, 2, 3, 4, 5, 6, 7, 9, 11, 13, 14, 21, 23, 41, 46, 89, 110, 389, 413, 489, 869, 1589, 1713, 2831, 10843, 11257, 16949, 24513, 39621, 43349, 62941, 96094, 139237, 145289, 264683, 396790

Offset: 1

Author

Robert G. Wilson v, Sep 16 2000

Keywords

• nonn

Comments

The first four terms correspond to negative primes. Dropping them gives A096820. - Joerg Arndt, Oct 05 2012

Crossrefs

Cf. A096820.

Programs

Mathematica

Do[ If[ PrimeQ[ 2^n - 21 ], Print[ n ] ], {n, 1, 3000} ]

PARI

is(n)=isprime(2^n - 21) \\ Charles R Greathouse IV, Aug 08 2016

Extensions

a(25)-a(34) from A096820, by Bruno Berselli, Oct 05 2012

a(35)-a(36) from A096820, by Robert Price, Aug 08 2016