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A032684 Numbers k such that k surrounded by digit '7' is prime. 2
2, 5, 8, 9, 12, 17, 18, 20, 23, 24, 29, 30, 41, 45, 47, 48, 50, 51, 53, 54, 57, 60, 68, 71, 72, 75, 81, 86, 87, 90, 92, 93, 114, 116, 123, 125, 128, 131, 132, 134, 138, 143, 152, 153, 159, 164, 170, 177, 180, 183, 186, 188, 191, 194, 198, 204, 207 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Daniel Starodubtsev, Table of n, a(n) for n = 1..10000

PROG

(Python)

from sympy import isprime

print([i for i in range(200) if isprime(int('7' + str(i) + '7'))]) # Daniel Starodubtsev, Apr 05 2020

CROSSREFS

Cf. A032689.

Sequence in context: A045928 A190768 A184866 * A026448 A258353 A050678

Adjacent sequences:  A032681 A032682 A032683 * A032685 A032686 A032687

KEYWORD

nonn,base

AUTHOR

Patrick De Geest, May 15 1998

STATUS

approved

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Last modified March 6 04:14 EST 2021. Contains 341841 sequences. (Running on oeis4.)