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%I #11 Oct 30 2019 23:48:08
%S 29,22929299,29229929,29299229,29992229,92922299,99292229,2229922999,
%T 2229929929,2229992299,2292229999,2292929299,2292999229,2299222999,
%U 2299292929,2299922929,2922929929,2922992299,2929292299,2929299229
%N Primes consisting only of digits 2 and 9 occurring with equal frequency.
%C 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).
%C The number of digits in a term is even but not a multiple of 6. - _Robert Israel_, Oct 30 2019
%H Robert Israel, <a href="/A087528/b087528.txt">Table of n, a(n) for n = 1..6235</a>
%p F:= proc(d) local C,c;
%p if d mod 3 = 0 then return NULL fi;
%p C:= map(t -> [0,op(t)], combinat:-choose([$1..d-1],d/2-1));
%p C:= map(t -> 2*(10^d-1)/9 + 7*add(10^c,c=t), C);
%p op(sort(select(isprime,C)))
%p end proc:
%p seq(F(d),d=2..14,2); # _Robert Israel_, Oct 30 2019
%Y Cf. A087510, A087511, A087514.
%K base,nonn
%O 1,1
%A _Paul D. Hanna_ and _Amarnath Murthy_, Sep 12 2003
%E Offset corrected by _Robert Israel_, Oct 30 2019
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