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A278418
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Numbers k such that (83*10^k - 29) / 9 is prime.
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0
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1, 2, 4, 10, 28, 31, 32, 38, 68, 134, 158, 254, 311, 337, 392, 874, 2747, 3502, 4735, 6142, 14140, 17095, 20066, 21104, 26743
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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 9 followed by k-2 occurrences of the digit 2 followed by the digits 19 is prime (see Example section).
a(26) > 2*10^5.
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LINKS
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Table of n, a(n) for n=1..25.
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 92w19.
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EXAMPLE
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4 is in this sequence because (83*10^4 - 29) / 9 = 92219 is prime.
Initial terms and primes associated:
a(1) = 1, 89;
a(2) = 2, 919;
a(3) = 4, 92219;
a(4) = 10, 92222222219;
a(5) = 28, 92222222222222222222222222219; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(83*10^# - 29) / 9] &]
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PROG
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(PARI) isok(n) = isprime((83*10^n - 29)/9); \\ Michel Marcus, Nov 21 2016
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CROSSREFS
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Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
Sequence in context: A005975 A048193 A123411 * A321946 A244485 A128933
Adjacent sequences: A278415 A278416 A278417 * A278419 A278420 A278421
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KEYWORD
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nonn,more,hard
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AUTHOR
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Robert Price, Nov 21 2016
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STATUS
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approved
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