A127942 a(n) = denominator of b(n), where b(1)=1, b(n) = Sum_{1<=k<n, gcd(k,n)=1} 1/b(k).

1, 1, 1, 2, 6, 19, 2850, 459458, 216537731091, 4850944054979611, 7043380548155783510819615297769488951475, 9278148088243438548919355731906562181020842484

Offset

1,4

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

Crossrefs

Cf. A127941.

Sequence in context: A341639 A186770 A332406 * A110956 A298446 A364563

Adjacent sequences: A127939 A127940 A127941 * A127943 A127944 A127945

Keyword

frac,nonn

Author

Leroy Quet, Feb 08 2007

Extensions

Extended by Ray Chandler, Feb 09 2007

Status

approved