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A293910
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Numbers k such that (26*10^k - 173)/3 is prime.
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0
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1, 2, 3, 8, 11, 13, 17, 28, 46, 67, 136, 536, 619, 746, 2420, 2672, 8228, 10861, 13424, 16047, 18075, 37720, 56371, 75055
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OFFSET
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1,2
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COMMENTS
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For k>1, numbers such that the digit 8 followed by k-2 occurrences of the digit 6 followed by the digits 09 is prime (see Example section).
a(25) > 2*10^5.
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LINKS
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Table of n, a(n) for n=1..24.
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 86w09.
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EXAMPLE
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2 is in this sequence because (26*10^2 - 173)/3 = 809 is prime.
Initial terms and primes associated:
a(1) = 1, 29;
a(2) = 2, 809;
a(3) = 3, 8609;
a(4) = 8, 866666609;
a(5) = 11, 866666666609; etc.
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MATHEMATICA
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Select[Range[1, 100000], PrimeQ[(26*10^# - 173)/3] &]
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CROSSREFS
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Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
Sequence in context: A201541 A084917 A134713 * A173269 A050557 A039000
Adjacent sequences: A293907 A293908 A293909 * A293911 A293912 A293913
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KEYWORD
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nonn,more,hard
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AUTHOR
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Robert Price, Oct 19 2017
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STATUS
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approved
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