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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
OFFSET
1,3
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
KEYWORD
frac,nonn
AUTHOR
Leroy Quet, Feb 08 2007
EXTENSIONS
Extended by Ray Chandler, Feb 09 2007
STATUS
approved