A087514 Primes consisting only of digits 1 and 7 occurring with equal frequency.

17, 71, 11171777, 11177717, 17111777, 17171177, 17171771, 17177117, 17711717, 17717171, 71117177, 71171717, 71717117, 77111717, 77711171, 1111717777, 1117117777, 1117177177, 1117771177, 1117771717, 1177117177, 1177177711, 1177711177, 1177717171, 1177717711

Offset: 1

Author

Amarnath Murthy and Paul D. Hanna, Sep 11 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..10444 (first 1001 terms from Harvey P. Dale)

Crossrefs

Cf. A087510, A087511, A087513.

Programs

Mathematica

Sort[Select[FromDigits/@Flatten[Table[Permutations[PadRight[{},2n,{1,7}]],{n,5}],1],PrimeQ]] (* Harvey P. Dale, Jul 27 2019 *)

PARI

\\ Needs B() from A087510.
concat(vector(6,k,B(k,1,7,isprime))) \\ Andrew Howroyd, Sep 21 2024

Extensions

Offset changed by Andrew Howroyd, Sep 21 2024