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A129457
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a(1)=1; a(n) = number of earlier terms of the sequence that are coprime to (n+a(n-1)).
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1
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1, 1, 2, 2, 4, 2, 6, 2, 8, 2, 10, 2, 10, 2, 14, 2, 16, 2, 16, 2, 20, 2, 19, 23, 4, 4, 26, 4, 27, 26, 27, 31, 7, 33, 9, 27, 11, 35, 13, 39, 14, 13, 14, 16, 44, 9, 15, 33, 19, 38, 50, 11, 21, 37, 22, 11, 24, 24, 58, 24, 54, 24, 45, 63, 26, 25, 26, 27, 15, 60, 70, 29, 16, 14, 74, 14, 59
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OFFSET
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1,3
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LINKS
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EXAMPLE
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13 + a(12) = 15. There are 10 terms among a(1),a(2)..,a(12) that are coprime to 15. (These terms are a(1),a(2),a(3),a(4),a(5),a(6),a(8),a(9), a(10) and a(12).) So a(13) = 10.
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MAPLE
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a[1]:=1: for n from 2 to 100 do ct:=0: for j from 1 to n-1 do if igcd(a[j], n+a[n-1])=1 then ct:=ct+1 else fi od: a[n]:=ct: od: seq(a[n], n=1..100); # Emeric Deutsch, Apr 17 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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