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A087535 Primes consisting only of digits 5 and 9 occurring with equal frequency. 2
59, 55599959, 99555959, 5555995999, 5559999559, 5595959959, 5595999559, 5599595959, 5599959559, 5955559999, 5955599959, 5959559959, 5959599559, 5995559599, 5995559959, 5995995559, 5999555959, 9555599959, 9555959599 (list; graph; refs; listen; history; text; internal format)
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

Table of n, a(n) for n=0..18.

MATHEMATICA

Sort[Flatten[Table[Select[FromDigits/@Permutations[Flatten[Table[{5, 9}, {n}]]], PrimeQ], {n, 5}]]] (* Harvey P. Dale, May 31 2013 *)

PROG

(PARI) \\ 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)

CROSSREFS

Cf. A087510, A087511, A087534.

Sequence in context: A191947 A188269 A093403 * A058931 A092914 A022083

Adjacent sequences:  A087532 A087533 A087534 * A087536 A087537 A087538

KEYWORD

base,nonn

AUTHOR

Paul D. Hanna and Amarnath Murthy, Sep 12 2003

STATUS

approved

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Last modified April 5 16:43 EDT 2020. Contains 333245 sequences. (Running on oeis4.)