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A165508 Numbers k such that 10^k + 111 is prime. 1
2, 4, 184, 460, 784, 3248, 5194, 92386 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Terms must be congruent to 2 or 4 mod 6. Other than the first term, which produces 10^2 + 111 = 211, these terms produce primes whose decimal representation is 1 <n-3 0's> 111 concatenated. These are only known to be highly probable primes for 184 and beyond. No more terms up to 15000.
a(8) > 55000. - Tyler NeSmith, Jul 10 2021
The corresponding primes have digit sum 4 (A062339). - Jeppe Stig Nielsen, Feb 10 2023
a(9) > 10^5. - Jeppe Stig Nielsen, Feb 11 2023
LINKS
EXAMPLE
As 10111 = 10^4 + 111 is a prime, 4 is a term.
MATHEMATICA
Select[Range[5200], PrimeQ[10^# + 111] &] (* G. C. Greubel, Oct 21 2018 *)
PROG
(PARI) is(k)=ispseudoprime(10^k+111) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
Sequence in context: A012369 A009609 A012367 * A018633 A307556 A018637
KEYWORD
nonn,more
AUTHOR
Rick L. Shepherd, Sep 21 2009
EXTENSIONS
a(8) from Jeppe Stig Nielsen, Feb 10 2023
STATUS
approved

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Last modified July 13 17:55 EDT 2024. Contains 374285 sequences. (Running on oeis4.)