A020466 Primes that contain digits 4 and 9 only.

449, 499, 4999, 9949, 44449, 49499, 49999, 94949, 94999, 444449, 994949, 999499, 4444949, 4449449, 4944949, 4949449, 4999949, 4999999, 9444949, 9494999, 9944449, 9994499, 44444999, 44499449, 44944499, 44994949, 49444949, 49444999, 49494499

Offset: 1

Author

David W. Wilson

Keywords

• nonn
• base

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..20000 (first 1000 terms from Vincenzo Librandi)
• James Maynard and Brady Haran, Primes without a 7, Numberphile video (2019)

Crossrefs

Cf. A036319 (composite numbers having all their prime factors in this sequence).

Programs

Mathematica

Flatten[Table[Select[FromDigits/@Tuples[{4,9},n],PrimeQ],{n,8}]] (* Vincenzo Librandi, Jul 27 2012 *)

PARI

is(N)=isprime(N)&&!#setminus(Set(digits(N)), [4,9]) \\ M. F. Hasler, Sep 22 2020