A020471 Primes that contain digits 7 and 9 only.

7, 79, 97, 797, 977, 997, 77797, 77977, 77999, 79777, 79979, 79997, 79999, 97777, 777977, 777979, 779797, 797977, 799979, 799999, 999979, 7777997, 7779979, 7779997, 7797799, 7797997, 7799797, 7799999, 7977779, 7977797, 7977799, 7977997

Offset: 1

Author

David W. Wilson

Keywords

• nonn
• base

Links

• Jason Bard, Table of n, a(n) for n = 1..10000 (first 1000 terms from Vincenzo Librandi)
• Index to entries about primes with digits in a given set

Crossrefs

Subsequence of A030096.

Cf. A020449 (digits 0 & 1), ..., A020472 (digits 8 & 9).

Programs

Magma

[p: p in PrimesUpTo(7977997) | Set(Intseq(p)) subset [7,9]]; // Vincenzo Librandi, Jul 28 2012

Mathematica

Flatten[Table[Select[FromDigits/@Tuples[{7,9},n],PrimeQ],{n,7}]] (* Vincenzo Librandi, Jul 28 2012 *)

Extensions

Edited by M. F. Hasler, Jul 26 2015