A087535 Primes consisting only of digits 5 and 9 occurring with equal frequency.

59, 55599959, 99555959, 5555995999, 5559999559, 5595959959, 5595999559, 5599595959, 5599959559, 5955559999, 5955599959, 5959559959, 5959599559, 5995559599, 5995559959, 5995995559, 5999555959, 9555599959, 9555959599, 9555995959, 9555999559, 9559595599

Offset: 1

Author

Paul D. Hanna and Amarnath Murthy, 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..5353

Crossrefs

Cf. A087510, A087511, A087534.

Programs

Mathematica

Sort[Flatten[Table[Select[FromDigits/@Permutations[Flatten[Table[{5,9},{n}]]],PrimeQ],{n,5}]]] (* Harvey P. Dale, May 31 2013 *)

PARI

\\ Needs B() from A087510.
concat(vector(6,k,B(k,5,9,isprime))) \\ Andrew Howroyd, Sep 20 2024

Extensions

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