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A127942
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a(n) = denominator of b(n), where b(1)=1, b(n) = sum{1<=k<n,GCD(k,n)=1} 1/b(k).
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1
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1, 1, 1, 2, 6, 19, 2850, 459458, 216537731091, 4850944054979611, 7043380548155783510819615297769488951475, 9278148088243438548919355731906562181020842484
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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EXAMPLE
| {b(n)}: 1,1,2,3/2,19/6,25/19,12091/2850,... Since 1 and 5 are the positive integers which are coprime to 6 and are < 6, then b(6) = 1/b(1) + 1/b(5) = 1 + 6/19 = 25/19.
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MATHEMATICA
| f[l_List] := Block[{n = Length[l] + 1, d}, d = Select[Range[n - 1], GCD[ #, n] == 1 &]; Append[l, Sum[1/l[[d[[i]]]], {i, Length[d]}]]]; Denominator[Nest[f, {1}, 12]] (*Chandler*)
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CROSSREFS
| Cf. A127941.
Sequence in context: A079564 A079453 A186770 * A110956 A205012 A028689
Adjacent sequences: A127939 A127940 A127941 * A127943 A127944 A127945
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KEYWORD
| frac,nonn
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AUTHOR
| Leroy Quet Feb 08 2007
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EXTENSIONS
| Extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), Feb 09 2007
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