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Search: id:A130180
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| A130180 |
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Number of numbers k > 1 such that (sum of digits of k^n)*(sum of digits of k^(n+1)) = k. |
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3
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| 5, 3, 12, 2, 6, 8, 4, 1, 13, 8, 7, 14, 8, 3, 9, 1, 5, 12, 4, 0, 13, 4, 7, 7, 1, 4, 7, 2, 5, 8, 2, 4, 8, 7, 1, 10, 5, 2, 8, 4, 2, 10, 2, 6, 10, 2, 3, 6, 2, 4, 4, 2, 3, 9
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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80, 1036, 1215 are the only numbers k > 1 such that (sum of digits of k^2)*(sum of digits of k^3 = k, hence a(2) = 3.
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CROSSREFS
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Cf. A126783 (smallest k), A130179 (upper bound), A130181 (largest k).
Sequence in context: A137613 A165670 A141234 this_sequence A104587 A131939 A111744
Adjacent sequences: A130177 A130178 A130179 this_sequence A130181 A130182 A130183
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KEYWORD
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nonn,base,hard,more
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AUTHOR
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Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), May 14 2007
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