A087534 Primes consisting only of digits 4 and 9 occurring with equal frequency.

44994949, 49444999, 49494499, 49499449, 94449499, 4449449999, 4449494999, 4494494999, 4494499949, 4494949499, 4494994499, 4499449949, 4499494949, 4499944949, 4944499949, 4949444999, 4994449949, 9444499949, 9444994499

Offset

0,1

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).

Links

Harvey P. Dale, Table of n, a(n) for n = 0..10000

Mathematica

Sort[Flatten[Table[Select[FromDigits/@Permutations[PadRight[{}, 2n, {4, 9}]], PrimeQ], {n, 5}]]] (* Harvey P. Dale, Aug 21 2016 *)

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)

Crossrefs

Cf. A087510, A087511, A087533.

Sequence in context: A130913 A213353 A205263 * A183747 A112444 A083630

Adjacent sequences: A087531 A087532 A087533 * A087535 A087536 A087537

Keyword

base,nonn

Author

Paul D. Hanna and Amarnath Murthy, Sep 12 2003

Extensions

Edited by Charles R Greathouse IV, Oct 28 2009

Status

approved