A032684 - OEIS

A032684

Numbers k such that k surrounded by digit '7' is prime.

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 A173286

Adjacent sequences: A032681 A032682 A032683 * A032685 A032686 A032687

KEYWORD

nonn,base

AUTHOR

Patrick De Geest, May 15 1998

STATUS

approved