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A109137
Numbers k such that k * (10^k - 1) + 1 is prime.
0
2, 14, 42, 144, 200, 302, 7242, 8718, 10568, 24438, 41734
OFFSET
1,1
COMMENTS
Larger values certified with ECM. No more up to 6000.
PROG
(PARI) is(n)=ispseudoprime(n*(10^n-1)+1) \\ Charles R Greathouse IV, Jun 13 2017
(Python)
from sympy import isprime
def afind(limit, startk=1):
k, pow10 = startk, 10**startk
for k in range(startk, limit+1):
if isprime(k*(pow10 - 1) + 1): print(k, end=", ")
k += 1
pow10 *= 10
afind(500) # Michael S. Branicky, Aug 26 2021
CROSSREFS
Cf. A110807.
Sequence in context: A231081 A364218 A152670 * A192375 A267247 A297425
KEYWORD
more,nonn
AUTHOR
Jason Earls, Aug 18 2005
EXTENSIONS
a(7)-a(8) from Ryan Propper, Sep 20 2006
a(9) from Michael S. Branicky, Aug 26 2021
a(10) from Michael S. Branicky, Apr 05 2023
a(11) from Michael S. Branicky, Oct 17 2024
STATUS
approved