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
Offset: 1
Links
- Daniel Starodubtsev, Table of n, a(n) for n = 1..10000
Crossrefs
Cf. A032689.
Programs
-
Python
from sympy import isprime print([i for i in range(200) if isprime(int('7' + str(i) + '7'))]) # Daniel Starodubtsev, Apr 05 2020