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A294484 Numbers k such that 7*10^k + 69 is prime. 0
1, 2, 3, 6, 7, 8, 10, 12, 13, 21, 46, 68, 91, 153, 366, 1112, 1185, 1222, 7161, 20077, 33435, 40747, 99133, 108300, 136716 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 7 followed by k-2 occurrences of the digit 0 followed by the digits 69 is prime (see Example section).
a(26) > 2*10^5.
LINKS
Makoto Kamada, Search for 70w69.
EXAMPLE
2 is in this sequence because 7*10^2 + 69 = 769 is prime.
Initial terms and associated primes:
a(1) = 1, 139;
a(2) = 2, 769;
a(3) = 3, 7069;
a(4) = 6, 7000069;
a(5) = 7, 70000069; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[7*10^# + 69] &]
CROSSREFS
Sequence in context: A296350 A076436 A028768 * A064528 A366140 A179794
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Oct 31 2017
EXTENSIONS
a(24)-a(25) from Robert Price, Jul 09 2019
STATUS
approved

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Last modified June 22 09:21 EDT 2024. Contains 373568 sequences. (Running on oeis4.)