A138595 Numbers n such that 2^(2*n-21)-21 is prime.

11, 12, 13, 14, 15, 16, 17, 21, 22, 31, 55, 205, 217, 255

Offset

1,1

Links

Table of n, a(n) for n=1..14.

Example

2^(2*13-21)-21=11, 2^(2*14-21)-21=107, 2^(2*15-21)-21=491, 2^(2*16-21)-21=2027, ...

Mathematica

q=21; For[i=q, i<=q, a={}; Do[x=2^(2*n-i)-i; If[PrimeQ[x], AppendTo[a, n]], {n, 10^2}]; Print["2^(2*n-", i, ")-", i, " ", a]; i=i+2]

Prog

(PARI) is(n)=isprime(2^(2*n-21)-21) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

Sequence in context: A297269 A296710 A297143 * A192271 A214423 A185300

Adjacent sequences: A138592 A138593 A138594 * A138596 A138597 A138598

Keyword

nonn,easy

Author

Vladimir Joseph Stephan Orlovsky, May 13 2008

Status

approved