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A087534
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Primes consisting only of digits 4 and 9 occurring with equal frequency.
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2
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44994949, 49444999, 49494499, 49499449, 94449499, 4449449999, 4449494999, 4494494999, 4494499949, 4494949499, 4494994499, 4499449949, 4499494949, 4499944949, 4944499949, 4949444999, 4994449949, 9444499949, 9444994499
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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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).
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PROG
| (PARI) /* Primes consisting only of digits x and y, occurring with equal frequency. */ x=4; y=9; 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)
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CROSSREFS
| Cf. A087510, A087511, A087533.
Sequence in context: A049360 A130913 A205263 * A183747 A112444 A083630
Adjacent sequences: A087531 A087532 A087533 * A087535 A087536 A087537
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KEYWORD
| base,nonn
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AUTHOR
| Paul D. Hanna (pauldhanna(AT)juno.com) and Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Sep 12 2003
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EXTENSIONS
| Edited by Charles R Greathouse IV (charles.greathouse(AT)case.edu), Oct 28 2009
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