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A283496
Numbers k such that (19*10^k - 37)/9 is prime.
0
1, 4, 6, 10, 16, 37, 60, 64, 78, 96, 166, 256, 1294, 1398, 2044, 2244, 5080, 7464, 8041, 17929, 18144, 29080, 32623
OFFSET
1,2
For k > 1, numbers k such that the digit 2 followed by k-2 occurrences of the digit 1 followed by the digits 07 is prime (see Example section).
a(24) > 2*10^5.
EXAMPLE
4 is in this sequence because (19*10^4 - 37)/9 = 21107 is prime.
Initial terms and associated primes:
a(1) = 1, 17;
a(2) = 4, 21107;
a(3) = 6, 2111107;
a(4) = 10, 21111111107;
a(5) = 16, 21111111111111107; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[(19*10^# - 37)/9] &]
PROG
(PARI) isok(n) = isprime((19*10^n - 37)/9); \\ Indranil Ghosh, Mar 09 2017
CROSSREFS
Sequence in context: A050887 A078642 A032416 * A117149 A344146 A361564
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Mar 08 2017
STATUS
approved

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Last modified September 20 00:39 EDT 2024. Contains 376015 sequences. (Running on oeis4.)