A087515 Primes consisting only of digits 1 and 9 occurring with equal frequency.

19, 11919199, 11919991, 19111999, 19199119, 19911919, 19991911, 91919911, 91999111, 99111919, 99119191, 99919111, 1111919999, 1111999199, 1191911999, 1191919991, 1191991991, 1191999119, 1199911919, 1199911991, 1199919191, 1199919911, 1911919199, 1911991919

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..10477

Crossrefs

Cf. A087510, A087511, A087514.

Programs

PARI

\\ Needs B() from A087510.
concat(vector(6,k,B(k,1,9,isprime))) \\ Andrew Howroyd, Sep 21 2024

Extensions

Offset changed and a(22) onwards from Andrew Howroyd, Sep 21 2024