A172411 Numbers k such that 2^k+9 and 2^k+27 are prime.

1, 2, 5, 10

Offset: 1

Author

Juri-Stepan Gerasimov, Feb 02 2010

Keywords

• nonn
• less
• more

Comments

No further terms between 10 and 5000. - R. J. Mathar, Feb 07 2010

No further terms to 100000. Expected number of remaining terms: (zeta(2) - 1 - 1/4 - ... - 1/100000^2)/log^2 2 ~= 0.00002. - Charles R Greathouse IV, Mar 25 2010

Examples

			a(1)=1 because 2^1+3^2=11 and 2^1+3^3=29 are prime.
		

Programs

Mathematica

Select[Range[10],AllTrue[2^#+{9,27},PrimeQ]&] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, May 28 2016 *)

PARI

is(n)=isprime(2^n+9) && isprime(2^n+27) \\ Charles R Greathouse IV, Sep 06 2016

Formula

A057196 INTERSECT A157007 - R. J. Mathar, Feb 07 2010