A087531 Primes consisting only of digits 3 and 7 occurring with equal frequency.

37, 73, 33373777, 33773737, 37373773, 37377337, 73337377, 73337773, 73373737, 73773373, 77337373, 77733373, 3337737737, 3337777337, 3377733773, 3733377377, 3733733777, 3737733773, 3773333777, 3773337377, 3773733737, 3777333773, 3777337337, 3777337373

Offset: 1

Author

Amarnath Murthy and Paul D. Hanna, Sep 12 2003

Keywords

• base
• nonn

Comments

There are 18 digit pairs which can produce such primes. (1,0),(1,3),(1,4),(1,6),(1,7),(1,9),(2,3),(2,9),(3,4),(3,5),(3,7),(3,8),(4,7),(4,9),(5,9),(6,7),(7,9),(8,9).

Links

• Andrew Howroyd, Table of n, a(n) for n = 1..9185

Crossrefs

Cf. A087510, A087511, A087530.

Programs

Mathematica

Select[Flatten[Table[FromDigits/@Permutations[Join[Table[3, {i}], Table[7, {i}]]], {i, 7}]], PrimeQ] (* from Harvey P. Dale *)

PARI

\\ Needs B() from A087510.
concat(vector(6,k,B(k,3,7,isprime))) \\ Andrew Howroyd, Sep 20 2024

Extensions

Edited by Charles R Greathouse IV, Oct 28 2009

Offset changed and a(23) onwards from Andrew Howroyd, Sep 20 2024