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Search: id:A161184
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| 1, 2, 4, 6, 3, 6, 9, 3, 6, 3, 9, 6, 9, 9, 3, 9, 6, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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It appears that a significant number of highly composite numbers have 9 as their digital root.
a(n)=9 for n>17 because for those n, the highly composite number A002182(n) is divisible by 9. [From T. D. Noe (noe(AT)sspectra.com), Jul 28 2009]
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FORMULA
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a(n)=A010888(A140645(n)). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jun 15 2009]
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EXAMPLE
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7560 is a highly composite number whose digital root is 9.
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MAPLE
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read("transforms3"): L := BFILETOLIST("b002182.txt") : A007953 := proc(n) add(d, d=convert(n, base, 10)) ; end: A010888 := proc(n) local a ; a := A007953(n) ; while a > 9 do a := A007953(a) ; od; a; end: for i from 1 to 200 do printf("%d, ", A010888(op(i, L))) ; od: [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jun 15 2009]
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CROSSREFS
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Cf. A002182
Sequence in context: A104492 A075075 A088178 this_sequence A140645 A117532 A057336
Adjacent sequences: A161181 A161182 A161183 this_sequence A161185 A161186 A161187
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KEYWORD
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nonn,base
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AUTHOR
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Parthasarathy Nambi (PachaNambi(AT)yahoo.com), Jun 05 2009
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EXTENSIONS
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Extended by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jun 15 2009
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