A127939 a(n) = numerator of b(n), where b(1)=1, b(n+1) = sum{k|n} 1/b(k).

1, 1, 2, 3, 8, 11, 71, 93, 319, 1143, 26821, 35965, 11013191, 13386881, 2977385045, 52264524083, 18887557655957, 23748158395676, 102452785866447, 126200944262123, 5090984756239094159, 1472248446028712283967

Offset

1,3

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]}]]]; Numerator[Nest[f, {1}, 22]] (* Ray Chandler, Feb 09 2007 *)

Crossrefs

Cf. A127940 (denominators).

Sequence in context: A056922 A101579 A041711 * A041587 A139447 A042783

Adjacent sequences: A127936 A127937 A127938 * A127940 A127941 A127942

Keyword

frac,nonn

Author

Leroy Quet, Feb 08 2007

Extensions

Extended by Ray Chandler, Feb 09 2007

Status

approved