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A342221
Integers k, not congruent to 1 mod 3, such that there is no prime of length k using digit 3 once and rest all 1.
0
15, 26, 32, 41, 68, 93, 99, 113, 116, 119, 134, 150, 158, 161, 170, 173, 176, 177, 179, 204, 213, 252, 257, 266, 284, 299, 305, 312, 320, 333, 353, 357, 374, 392, 402, 404, 419, 434, 443, 450, 491, 495, 506, 509, 513, 518, 527, 548, 551, 554, 570, 582, 584, 593
OFFSET
1,1
COMMENTS
The "not congruent to 1 mod 3" condition is due to the fact that A090537(3*k+1) = 0.
PROG
(Python)
from sympy import isprime
A342221_list = []
for k in range(1, 10**3):
if k % 3 != 1:
m, l = (10**k-1)//9, 2
for i in range(k):
if isprime(m+l):
break
l *= 10
else:
A342221_list.append(k) # Chai Wah Wu, Mar 15 2021
CROSSREFS
Subsequence of A007494.
Sequence in context: A146249 A248834 A249109 * A074974 A191913 A191915
KEYWORD
nonn,base
AUTHOR
Michel Marcus, Mar 14 2021
EXTENSIONS
More terms from Chai Wah Wu, Mar 15 2021
STATUS
approved