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A095370
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Number of distinct prime factors of the repunit (-1 + 10^n)/9.
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19
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0, 1, 2, 2, 2, 5, 2, 4, 3, 4, 2, 7, 3, 4, 6, 6, 2, 8, 1, 7, 7, 6, 1, 10, 5, 6, 5, 8, 5, 13, 3, 11, 6, 6, 7, 11, 3, 3, 6, 11, 4, 14, 4, 10, 9, 6, 2, 13, 4, 10, 8, 9, 4, 12, 8, 12, 6, 8, 2, 20, 7, 5, 13, 15, 7, 14, 3, 10, 6, 12, 2, 17, 3, 7, 12, 6, 8, 15, 6, 15, 10, 7, 3, 21, 7, 8, 10, 14, 5, 21, 12, 10
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OFFSET
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1,3
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COMMENTS
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Factoring certain repunits is especially difficult.
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REFERENCES
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Yates, S. "Peculiar Properties of Repunits." J. Recr. Math. 2, 139-146,1969.
Yates, S. "Prime Divisors of Repunits." J. Recr. Math. 8, 33-38, 1975.
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LINKS
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FORMULA
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EXAMPLE
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a(62)=5 because
11111111111111111111111111111111111111111111111111111111111111 =
11 * 2791 * 6943319 * 57336415063790604359 * 909090909090909090909090909091.
a(97)=3 because (10^97 - 1)/9 = 12004721 * 846035731396919233767211537899097169 * 109399846855370537540339266842070119107662296580348039.
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MATHEMATICA
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PROG
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CROSSREFS
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Cf. A046053 (total number of prime factors).
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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