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A127941 a(n) = numerator of b(n), where b(1)=1, b(n) = Sum_{1<=k<n, gcd(k,n)=1} 1/b(k). 1
1, 1, 2, 3, 19, 25, 12091, 942579, 802405765442, 9728923151534907, 40387361143971542769608346059516047956596, 16013133965687337121814734147004294320263129575 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Table of n, a(n) for n=1..12.

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, b(6) = 1/b(1) + 1/b(5) = 1 + 6/19 = 25/19.

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]}]]]; Numerator[Nest[f, {1}, 12]] (* Ray Chandler, Feb 09 2007 *)

CROSSREFS

Cf. A127942.

Sequence in context: A215388 A215361 A090476 * A195416 A215383 A215387

Adjacent sequences:  A127938 A127939 A127940 * A127942 A127943 A127944

KEYWORD

frac,nonn

AUTHOR

Leroy Quet, Feb 08 2007

EXTENSIONS

Extended by Ray Chandler, Feb 09 2007

STATUS

approved

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Last modified September 19 07:24 EDT 2020. Contains 337178 sequences. (Running on oeis4.)