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A295627
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Numbers k such that (397*10^k + 53)/9 is prime.
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0
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5, 9, 17, 47, 54, 75, 191, 207, 267, 894, 2099, 7164, 8625, 10865, 20394, 22251, 23088, 29015, 92369
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OFFSET
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1,1
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COMMENTS
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For k > 1, numbers such that the digits 44 followed by k-1 occurrences of the digit 1 followed by the digit 7 is prime (see Example section).
a(20) > 2*10^5.
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LINKS
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Table of n, a(n) for n=1..19.
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 441w7.
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EXAMPLE
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5 is in this sequence because (397*10^5 + 531)/9 = 4411117 is prime.
Initial terms and primes associated:
a(1) = 5, 4411117;
a(2) = 9, 44111111117;
a(3) = 17, 4411111111111111117; etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(397*10^# + 53)/9] &]
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CROSSREFS
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Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
Sequence in context: A099213 A146067 A336139 * A300128 A334993 A262484
Adjacent sequences: A295624 A295625 A295626 * A295628 A295629 A295630
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KEYWORD
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nonn,more,hard
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AUTHOR
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Robert Price, Nov 24 2017
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STATUS
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approved
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