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A067004
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Number of numbers <= n with same number of divisors as n.
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6
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1, 1, 2, 1, 3, 1, 4, 2, 2, 3, 5, 1, 6, 4, 5, 1, 7, 2, 8, 3, 6, 7, 9, 1, 3, 8, 9, 4, 10, 2, 11, 5, 10, 11, 12, 1, 12, 13, 14, 3, 13, 4, 14, 6, 7, 15, 15, 1, 4, 8, 16, 9, 16, 5, 17, 6, 18, 19, 17, 1, 18, 20, 10, 1, 21, 7, 19, 11, 22, 8, 20, 2, 21, 23, 12, 13, 24, 9, 22, 2, 2, 25, 23, 3, 26, 27
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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FORMULA
| Ordinal transform of A000005. - Frank Adams-Watters (FrankTAW(AT)Netscape.net), Aug 28 2006
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EXAMPLE
| a(10)=3 since 6,8,10 each have four divisors. a(11)=5 since 2,3,5,7,11 each have two divisors.
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CROSSREFS
| Cf. A000005, A008479, A058933, A067003. Inverse of A000040, A001248, A030513, A030514, A030515, A030516, A030626, A030627,
A030628, A030629, A030630, A030631, A030632, A030633, A030634, A030635, A030636, A030637, A030638 etc.
Cf. also A079788, A138009.
A047983(n) = a(n)-1.
Sequence in context: A132460 A067734 A161904 * A117920 A079617 A079616
Adjacent sequences: A067001 A067002 A067003 * A067005 A067006 A067007
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KEYWORD
| nonn
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AUTHOR
| Henry Bottomley (se16(AT)btinternet.com), Dec 21 2001
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