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A087533
Primes consisting only of digits 4 and 7 occurring with equal frequency.
4
47, 47447747, 77474447, 4447747747, 4744477747, 4744747477, 4744747747, 4747444777, 4747747447, 4774744477, 4774747447, 7444477477, 7447474477, 7744744747, 7744747447, 7747444477, 7747447447, 7747744447, 44444477777477, 44447447774777, 44447474777477
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
MATHEMATICA
Table[Select[FromDigits/@Permutations[PadRight[{}, 2n, {4, 7}]], PrimeQ], {n, 7}]//Flatten//Sort (* Harvey P. Dale, May 05 2016 *)
PROG
(PARI) \\ Needs B() from A087510.
concat(vector(6, k, B(k, 4, 7, isprime))) \\ Andrew Howroyd, Sep 20 2024
CROSSREFS
KEYWORD
base,nonn
AUTHOR
EXTENSIONS
Edited by Charles R Greathouse IV, Oct 28 2009
Corrected by Harvey P. Dale, May 05 2016
Offset changed by Andrew Howroyd, Sep 20 2024
STATUS
approved