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A127792
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a(0)=1; for n>0, a(n) = Sum_{k|n} (number of earlier terms which are coprime to k).
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1
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1, 1, 4, 6, 8, 10, 15, 14, 17, 23, 27, 22, 41, 26, 41, 51, 52, 32, 67, 38, 76, 74, 63, 45, 99, 69, 78, 81, 112, 58, 138, 62, 107, 107, 98, 126, 154, 73, 110, 127, 184, 80, 193, 86, 162, 207, 126, 94, 213, 133, 205, 169, 198, 106, 235, 197, 260, 188, 169, 118, 364, 122, 179
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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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The positive divisors of 8 are 1,2,4,8. So a(8) = (the number of earlier terms coprime to 1, which is 8) + (the number of earlier terms coprime to 2, which is 3 for a(0)=1, a(1)=1 and a(6) = 15) + (the number of earlier terms coprime to 4, which is 3) + (the number of earlier terms coprime to 8, which is 3) = 8 + 3 + 3 + 3 = 17.
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MATHEMATICA
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f[l_List] := Block[{n = Length[l], d = Divisors[n], c = 0}, Do[ c += Length[Select[l, GCD[ #, d[[i]]] == 1 &]]; , {i, Length[d]}]; Append[l, c]]; Nest[f, {1}, 64] (* Ray Chandler, Feb 08 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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