A036945 Smallest n-digit prime containing only the digits 4 and 9, or 0 if no such prime exists.

0, 0, 449, 4999, 44449, 444449, 4444949, 44444999, 444499949, 4444444999, 44444449949, 444444494449, 4444449444949, 44444444449499, 444444444499499, 4444444444444999, 44444444444444999, 444444444449449949

Offset: 1

Author

Patrick De Geest, Jan 04 1999

Keywords

• nonn
• base

Examples

			44449 is the least prime of 5 digits containing just digits 4 and 9 so a(5) = 44449. - _David A. Corneth_, Oct 10 2019
		

Links

• David A. Corneth, Table of n, a(n) for n = 1..538

Crossrefs

Cf. A036229, A020466, A036319, A036929-A036951.

Programs

Mathematica

Join[{0,0},Table[SelectFirst[10*FromDigits[#]+9&/@Tuples[{4,9},n],PrimeQ],{n,2,20}]] (* Harvey P. Dale, Aug 20 2021 *)

PARI

a(n) = my(s=4*(10^(n)-1)/9);forstep(i=1, 2^n-1, 2, fr = fromdigits(5 * binary(i)) + s; if(isprime(fr), return(fr))); 0 \\ David A. Corneth, Oct 10 2019