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Search: id:A122169
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| A122169 |
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a(1)=1. a(n) = sum of earlier terms, a(k) (1<=k<=n-1), where GCD(a(k),n) is squarefree. |
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+0
2
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| 1, 1, 2, 4, 8, 16, 32, 4, 68, 136, 272, 4, 548, 1096, 2192, 4, 4388, 8776, 17552, 4, 35108, 70216, 140432, 4, 280868, 561736, 1123472, 4, 2246948, 4493896, 8987792, 4, 17975588, 35951176, 71902352, 4, 143804708, 287609416, 575218832, 4
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OFFSET
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1,3
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EXAMPLE
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(1,1,2,4,4,4,4,4,4,4,4) is GCD(a(k),12), for 1 <=k <=11. Of these integers, only the first 3 are squarefree, so a(12) = a(1)+a(2)+a(3) = 4.
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MATHEMATICA
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sf[n_] := Max @@ Last /@ FactorInteger[n] < 2; f[s_] := Append[s, Plus @@ Select[s, sf[GCD[ #, Length[s] + 1]] &]]; Nest[f, {1}, 40] (*Chandler*)
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CROSSREFS
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Cf. A122168.
Sequence in context: A018487 A010747 A036130 this_sequence A114183 A036129 A088976
Adjacent sequences: A122166 A122167 A122168 this_sequence A122170 A122171 A122172
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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), Aug 23 2006
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EXTENSIONS
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Extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), Aug 24 2006
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