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A032683
Numbers k such that k surrounded by digit '3' is a prime.
5
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
1,2
LINKS
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
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Patrick De Geest, May 15 1998
STATUS
approved