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A281167 Numbers k such that (23*10^k - 143)/3 is prime. 0
1, 2, 6, 7, 14, 22, 31, 33, 42, 51, 799, 934, 1996, 3372, 3570, 3883, 4417, 4747, 4965, 5055, 5647, 7183, 19702, 42124, 180862, 187164 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
For k>1, numbers such that the digit 7 followed by k-2 occurrences of the digit 6 followed by the digits 19 is prime (see Example section).
a(27) > 2*10^5.
LINKS
Makoto Kamada, Search for 76w19.
EXAMPLE
2 is in this sequence because (23*10^2 - 143) / 3 = 719 is prime.
Initial terms and primes associated:
a(1) = 1, 29;
a(2) = 2, 719;
a(3) = 6, 7666619;
a(4) = 7, 76666619;
a(5) = 14, 766666666666619; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(23*10^# - 143) / 3] &]
CROSSREFS
Sequence in context: A199974 A176279 A265739 * A210660 A344343 A226965
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Jan 16 2017
EXTENSIONS
a(25)-a(26) from Robert Price, Dec 04 2019
STATUS
approved

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Last modified March 29 03:41 EDT 2024. Contains 371264 sequences. (Running on oeis4.)