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

1,3

Links

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

Example

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

Mathematica

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

Prog

(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

Crossrefs

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

Sequence in context: A160291 A193255 A283791 * A201182 A012169 A093402

Adjacent sequences: A036942 A036943 A036944 * A036946 A036947 A036948

Keyword

nonn,base

Author

Patrick De Geest, Jan 04 1999

Status

approved