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A087512
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Primes consisting only of digits 1 and 4 occurring with equal frequency.
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3
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41, 14441411, 41414411, 44114141, 1144141441, 1144144411, 1144441141, 1411414441, 1441411441, 1441444111, 1444114141, 4111144441, 4111444411, 4114414141, 4141141441, 4141144141, 4144111441, 4411114441, 4411144141
(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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MAPLE
| 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
| Cf. A087510, A087513, A087514.
Sequence in context: A078813 A112550 A114927 * A125194 A095189 A023932
Adjacent sequences: A087509 A087510 A087511 * A087513 A087514 A087515
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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 11 2003
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