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A087514
Primes consisting only of digits 1 and 7 occurring with equal frequency.
5
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
1,1
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)
MATHEMATICA
Sort[Select[FromDigits/@Flatten[Table[Permutations[PadRight[{}, 2n, {1, 7}]], {n, 5}], 1], PrimeQ]] (* Harvey P. Dale, Jul 27 2019 *)
PROG
(PARI) \\ Needs B() from A087510.
concat(vector(6, k, B(k, 1, 7, isprime))) \\ Andrew Howroyd, Sep 21 2024
CROSSREFS
KEYWORD
base,nonn
AUTHOR
EXTENSIONS
Offset changed by Andrew Howroyd, Sep 21 2024
STATUS
approved