A032683 Numbers k such that k surrounded by digit '3' is a prime.

1, 5, 7, 8, 16, 20, 25, 31, 32, 34, 37, 41, 43, 46, 53, 58, 59, 61, 62, 64, 67, 73, 79, 80, 82, 83, 85, 86, 92, 94, 101, 103, 106, 112, 115, 118, 119, 122, 125, 133, 139, 151, 154, 157, 158, 164, 166, 172, 179, 187, 188, 196, 197, 200, 206, 208, 214, 217

Offset: 1

Author

Patrick De Geest, May 15 1998

Keywords

• nonn
• base

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A032682, A032684, A032685, A032687.

Programs

Mathematica

Select[Range[250],PrimeQ[FromDigits[Join[{3},IntegerDigits[#],{3}]]]&] (* Harvey P. Dale, Apr 18 2012 *)

Python

from sympy import isprime
def ok(n): return isprime(int('3' + str(n) + '3'))
print([k for k in range(220) if ok(k)]) # Michael S. Branicky, Sep 04 2022