A127940 a(n) = denominator of b(n), where b(1)=1, b(n+1) = sum{k|n} 1/b(k).

1, 1, 1, 2, 3, 8, 22, 71, 93, 638, 9144, 26821, 2373690, 11013191, 950468551, 23819080360, 4860600739719, 18887557655957, 23748158395676, 102452785866447, 1153981434332852712, 722919835385951370578

Offset

1,4

Links

G. C. Greubel, Table of n, a(n) for n = 1..68

Example

{b(n)}:1,1,2,3/2,8/3,11/8,71/22,93/71,...So b(7) = sum{k|6} 1/b(k) = 1/b(1) + 1/ b(2) + 1/b(3) + 1/b(6) = 1 + 1 + 1/2 + 8/11 = 71/22.

Mathematica

f[l_List] := Block[{n = Length[l], d = Divisors[n]}, Append[l, Sum[1/l[[d[[i]]]], {i, Length[d]}]]]; Denominator[Nest[f, {1}, 22]] (* Ray Chandler, Feb 09 2007 *)

Crossrefs

Cf. A127939 (numerators).

Sequence in context: A049959 A006545 A089402 * A006796 A241904 A006076

Adjacent sequences: A127937 A127938 A127939 * A127941 A127942 A127943

Keyword

frac,nonn

Author

Leroy Quet, Feb 08 2007

Extensions

Extended by Ray Chandler, Feb 09 2007

Status

approved