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%I #11 Dec 05 2013 20:16:11
%S 53,35553533,53355353,53533553,3335553553,3355335553,3355355533,
%T 3355533553,3355535353,3535355353,3553535353,3553555333,3555353353,
%U 3555353533,3555533533,5353353553,5353533553,5353553533,5355353533
%N Primes consisting only of digits 3 and 5 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).
%H Harvey P. Dale, <a href="/A087530/b087530.txt">Table of n, a(n) for n = 1..5000</a>
%t Sort[Select[FromDigits/@Flatten[Permutations/@Table[PadRight[{},2n,{3,5}],{n,5}],1],PrimeQ]] (* _Harvey P. Dale_, Oct 24 2012 *)
%o (PARI) /* Primes consisting only of digits x and y, occurring with equal frequency. */ x=3; y=5; d1=x; d2=y; k=0; a=vector(100); for(n=1,3000,B=binary(n); L=length(B); s=sum(j=1,length(B),B[j]); if(L%2==0 & s==L/2, C=vector(L,n,(d2-d1)*B[n]+d1); p=subst(Pol(C),x,10); if(isprime(p),if(k<100,k++; a[k]=p)); D=vector(L,n,d2-(d2-d1)*B[n]); q=subst(Pol(D),x,10); if(isprime(q ),if(k<100,k++; a[k]=q))); ); a=vector(k,n,a[n]); vecsort(a)
%Y Cf. A087510, A087511, A087529.
%K base,nonn
%O 1,1
%A _Amarnath Murthy_ and _Paul D. Hanna_, Sep 12 2003
%E Edited by _Charles R Greathouse IV_, Oct 28 2009
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