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Search: id:A087511
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| A087511 |
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Primes consisting only of digits 1 and 3 occurring with equal frequency. |
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+0
14
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| 13, 31, 11313331, 11333131, 13111333, 13131133, 13131331, 13133311, 13311313, 31133131, 33113131, 1113131333, 1131131333, 1131311333, 1131331133, 1133111333, 1133113133, 1133133311, 1133311313, 1133313113, 1133313131
(list; graph; listen)
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OFFSET
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0,1
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COMMENT
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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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MAPLE
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Primes consisting only of digits x and y, occurring with equal frequency. 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
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Cf. A087510, A087512, A087513.
Sequence in context: A007628 A104151 A023304 this_sequence A118513 A140678 A050659
Adjacent sequences: A087508 A087509 A087510 this_sequence A087512 A087513 A087514
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KEYWORD
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base,nonn
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AUTHOR
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Paul D. Hanna (pauldhanna(AT)juno.com) and Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Sep 11 2003
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