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A032685
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Numbers k such that k surrounded by digit '9' is a prime.
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8
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1, 2, 10, 19, 20, 23, 31, 34, 41, 43, 47, 53, 61, 62, 64, 67, 68, 71, 73, 74, 76, 82, 83, 85, 92, 94, 100, 101, 107, 109, 112, 113, 115, 119, 122, 124, 130, 136, 145, 149, 152, 163, 190, 193, 196, 200, 211, 217, 218, 221, 226, 236, 239, 241, 245
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,2
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LINKS
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Harvey P. Dale, Table of n, a(n) for n = 1..1000
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MATHEMATICA
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Select[Range[300], PrimeQ[FromDigits[Join[{9}, IntegerDigits[#], {9}]]]&] (* Harvey P. Dale, Jul 20 2012 *)
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PROG
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(Python)
from sympy import isprime
def ok(n): return isprime(int('9' + str(n) + '9'))
print([k for k in range(250) if ok(k)]) # Michael S. Branicky, Sep 04 2022
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CROSSREFS
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Cf. A032682, A032683, A032684, A032690.
Sequence in context: A330083 A322951 A156446 * A085936 A226179 A030570
Adjacent sequences: A032682 A032683 A032684 * A032686 A032687 A032688
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KEYWORD
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nonn,base
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AUTHOR
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Patrick De Geest, May 15 1998
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STATUS
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approved
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