A087528 Primes consisting only of digits 2 and 9 occurring with equal frequency.

29, 22929299, 29229929, 29299229, 29992229, 92922299, 99292229, 2229922999, 2229929929, 2229992299, 2292229999, 2292929299, 2292999229, 2299222999, 2299292929, 2299922929, 2922929929, 2922992299, 2929292299, 2929299229

Offset

1,1

Comments

There are 18 digit pairs which can produce such primes. (1,0),(7,0),(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).

The number of digits in a term is even but not a multiple of 6. - Robert Israel, Oct 30 2019

Links

Robert Israel, Table of n, a(n) for n = 1..6235

Maple

F:= proc(d) local C, c;
   if d mod 3 = 0 then return NULL fi;
   C:= map(t -> [0, op(t)], combinat:-choose([$1..d-1], d/2-1));
   C:= map(t -> 2*(10^d-1)/9 + 7*add(10^c, c=t), C);
   op(sort(select(isprime, C)))
end proc:
seq(F(d), d=2..14, 2); # Robert Israel, Oct 30 2019

Crossrefs

Cf. A087510, A087511, A087514.

Sequence in context: A321666 A139775 A303734 * A307622 A219015 A144839

Adjacent sequences: A087525 A087526 A087527 * A087529 A087530 A087531

Keyword

base,nonn

Author

Paul D. Hanna and Amarnath Murthy, Sep 12 2003

Extensions

Offset corrected by Robert Israel, Oct 30 2019

Status

approved