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Search: id:A127791
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| A127791 |
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a(1)=1; for n>1, a(n) = Sum_{k|n} (number of earlier terms which are coprime to k). |
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2
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| 1, 2, 4, 5, 7, 16, 11, 19, 24, 26, 19, 45, 23, 40, 47, 51, 31, 74, 34, 75, 70, 64, 43, 111, 62, 77, 89, 111, 56, 150, 58, 116, 110, 97, 115, 185, 68, 110, 136, 173, 80, 212, 83, 166, 209, 132, 91, 258, 134, 187, 173, 202, 103, 278, 182, 257, 200, 168, 116, 383, 120, 177
(list; graph; listen)
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OFFSET
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1,2
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LINKS
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Leroy Quet, Home Page (listed in lieu of email address)
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EXAMPLE
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Since the positive divisors of 10 are 1,2,5,10, a(10) = (the number of earlier terms coprime to 1, which is 9) + (the number of earlier terms coprime to 2, which is 5 for a(1)=1, a(4)=5, a(5)=7, a(7)=11 and a(8)=19) + (the number of earlier terms coprime to 5, which is 8 for every earlier term except a(4)=5) + (the number of earlier terms coprime to 10, which is 4) = 9 + 5 + 8 + 4 = 26.
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MATHEMATICA
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f[l_List] := Block[{n = Length[l] + 1, d = Divisors[n], c = 0}, Do[ c += Length[Select[l, GCD[ #, d[[i]]] == 1 &]]; , {i, Length[d]}]; Append[l, c]]; Nest[f, {1}, 64] (*Chandler*)
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CROSSREFS
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Cf. A127792.
Sequence in context: A123210 A101724 A019277 this_sequence A005620 A049915 A119909
Adjacent sequences: A127788 A127789 A127790 this_sequence A127792 A127793 A127794
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet Jan 29 2007
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EXTENSIONS
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Extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), Feb 08 2007
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