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A123273
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a(0) = 1; a(n) = the number of earlier terms, a(k), where gcd(a(k), a(floor(k/2))) = 1.
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1
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1, 1, 2, 3, 4, 4, 4, 5, 6, 6, 6, 6, 6, 6, 6, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 9, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 11, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12
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OFFSET
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0,3
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LINKS
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EXAMPLE
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Among terms a(0) through a(8) (1,1,2,3,4,4,4,5,6), a(0) is coprime to a(0), a(1) is coprime to a(0), a(2) is coprime to a(1), a(3) is coprime to a(1), a(6) is coprime to a(3) and a(7) is coprime to a(3). There are 6 such coprime pairs in the range, so a(9) = 6.
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MATHEMATICA
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f[l_List] := Append[l, Count[Table[GCD[l[[k]], l[[Floor[(k + 1)/2]]]], {k, Length[l]}], 1]]; Nest[f, {1}, 80] (* Ray Chandler, Oct 17 2006 *)
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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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