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A290150
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Numbers k such that (316*10^k - 1)/9 is prime.
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0
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2, 3, 8, 9, 11, 14, 17, 23, 29, 38, 50, 129, 164, 578, 1592, 2951, 4505, 16826, 17438, 22748
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OFFSET
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1,1
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COMMENTS
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Numbers such that the digits 35 followed by k occurrences of the digit 1 is prime (see Example section).
a(21) > 2*10^5.
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LINKS
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Table of n, a(n) for n=1..20.
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 351w.
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EXAMPLE
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3 is in this sequence because (316*10^3 - 1)/9 = 35111 is prime.
Initial terms and primes associated:
a(1) = 2, 3511;
a(2) = 3, 35111;
a(3) = 8, 3511111111;
a(4) = 9, 35111111111;
a(5) = 11, 3511111111111; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(316*10^# - 1)/9] &]
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CROSSREFS
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Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
Sequence in context: A028821 A337261 A288740 * A237037 A283618 A284370
Adjacent sequences: A290147 A290148 A290149 * A290151 A290152 A290153
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KEYWORD
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nonn,more,hard
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AUTHOR
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Robert Price, Jul 21 2017
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STATUS
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approved
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