A214705 Primes that contain only the digits (2, 5, 7).

2, 5, 7, 227, 257, 277, 557, 577, 727, 757, 2557, 2777, 5227, 5527, 5557, 7577, 7727, 7757, 22277, 22727, 22777, 25577, 27277, 27527, 52727, 52757, 57527, 57557, 57727, 72227, 72277, 72577, 72727, 75227, 75277, 75527, 75557, 75577, 77527, 77557, 222527, 222557

Offset: 1

Author

Vincenzo Librandi, Jul 28 2012

Keywords

• nonn
• base
• easy

Comments

The digits are prime numbers.

Links

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

Crossrefs

Subsequence of A019546.

Cf. A385768 - A385800.

Programs

Magma

[p: p in PrimesUpTo(100000) | Set(Intseq(p)) subset [2,5,7]];

Mathematica

Flatten[Table[Select[FromDigits/@Tuples[{2,5,7},n],PrimeQ],{n,6}]]

Python

from sympy import primerange
def ok(p): return set(str(p)) <= set("257")
def aupto(limit): return [p for p in primerange(2, limit+1) if ok(p)]
print(aupto(222557)) # Michael S. Branicky, Feb 05 2021