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Search: id:A125597
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| A125597 |
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a(1)=1. a(n) = sum{1<=k<n, GCD(k,n(n+1)/2)=1} a(k). |
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+0
2
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| 1, 1, 1, 2, 4, 8, 6, 11, 21, 51, 11, 22, 133, 159, 151, 328, 707, 1414, 880, 1732, 3850, 9482, 1742, 3480, 22126, 37243, 25604, 51381, 102087, 204174, 157324, 285010, 660221, 1285026, 262885, 547906, 3664304, 5844380, 3927062, 8543954, 19956539
(list; graph; listen)
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OFFSET
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1,4
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EXAMPLE
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The positive integers < 8 and coprime to 8*9/2 = 36 are 1,5,7. So a(8) = a(1)+a(5)+a(7) = 1+4+6 = 11.
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MATHEMATICA
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f[l_List] := Block[{n = Length[l] + 1}, Append[l, Plus @@ l[[Select[Range[n - 1], GCD[ #, n*(n + 1)/2] == 1 &]]]]]; Nest[f, {1}, 40] (*Chandler*)
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CROSSREFS
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Cf. A125596.
Adjacent sequences: A125594 A125595 A125596 this_sequence A125598 A125599 A125600
Sequence in context: A138284 A022478 A121711 this_sequence A109554 A140692 A048640
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet (qq-quet(AT)mindspring.com), Nov 26 2006
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EXTENSIONS
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Extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), Nov 26 2006
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