A020453 Primes that contain digits 1 and 5 only.

5, 11, 151, 1151, 1511, 11551, 15511, 15551, 51151, 51511, 51551, 55511, 115151, 511111, 511151, 515111, 1111151, 1115551, 1155151, 1551551, 1555111, 5115511, 5151151, 5151551, 5155511, 5511151, 5511511, 5515151, 5551111, 15511151

Offset: 1

Author

David W. Wilson

Keywords

• nonn
• base

Comments

The first 8 terms are also primes when read backward, i.e. in A007500. See also A199325. - M. F. Hasler, Nov 05 2011

Links

• Jason Bard, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Vincenzo Librandi)

Crossrefs

Subsequence of A030096.

Programs

Mathematica

Flatten[Table[Select[FromDigits/@Tuples[{1,5},n],PrimeQ],{n,7}]] (* Vincenzo Librandi, Jul 27 2012 *)

PARI

{L=[1,5];for(d=1,9,u=vector(d,i,10^(d-i))~;forvec(v=vector(d,i,[1,#L]),ispseudoprime(t=vector(d,i,L[v[i]])*u)&print1(t",")))}  \\ M. F. Hasler, Nov 05 2011