A032683 - OEIS

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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

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

MATHEMATICA

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

PROG

(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