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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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Larger values certified with ECM. No more up to 6000.
LINKS
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
STATUS
approved

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Last modified May 22 05:21 EDT 2024. Contains 372742 sequences. (Running on oeis4.)