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A128331
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a(1)=1. a(n) = number of positive numbers <= n that are coprime to a(n-1).
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0
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1, 2, 2, 2, 3, 4, 4, 4, 5, 8, 6, 4, 7, 12, 5, 13, 16, 9, 13, 19, 20, 9, 16, 12, 9, 18, 9, 19, 28, 13, 29, 31, 32, 17, 33, 22, 17, 36, 13, 37, 40, 17, 41, 43, 44, 21, 28, 21, 28, 21, 29, 51, 34, 25, 44, 25, 46, 28, 26, 28, 27, 42, 18, 21, 38, 31, 65, 51, 43, 69, 46, 34, 35, 52, 35
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OFFSET
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1,2
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LINKS
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EXAMPLE
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a(6) = 4. The number of positive integers <= 7 that are coprime to 4 is four, these integers being 1, 3, 5 and 7. So a(7) = 4.
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MATHEMATICA
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a = {1}; For[n = 2, n < 80, n++, in = 1; co = 0; While[in < n + 1, If[GCD[a[[ -1]], in] == 1, co++ ]; in++ ]; AppendTo[a, co]]; a (* Stefan Steinerberger, May 29 2007 *)
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CROSSREFS
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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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