A126262 a(n) is the denominator of the sum of the reciprocals of the positive integers k, k<=n, where every positive integer <= k and coprime to k is also coprime to n.

1, 2, 6, 4, 60, 3, 140, 24, 9, 20, 27720, 4, 360360, 84, 10, 560, 12252240, 36, 77597520, 10, 21, 1320, 118982864, 72, 50, 520, 7560, 42, 2329089562800, 15, 72201776446800, 1441440, 99, 9520, 420, 120, 485721041551200, 95760, 468, 24, 19914562703599200

Offset

1,2

Links

Table of n, a(n) for n=1..41.

Example

The positive integers k, k <= 6, where every positive integer <=k and coprime to k is also coprime to 6, are 1,2,6. So a(6) = 3 is the denominator of 1 +1/2 +1/6 = 5/3.

Mathematica

f[n_] := Select[Range[n], GCD[ #, n] == 1 &]; g[n_] := Plus @@ (1/# &) /@ Select[Range[n], Times @@ GCD[f[ # ], n] == 1 &]; Table[Denominator[g[n]], {n, 41}] (* Ray Chandler, Dec 24 2006 *)

Crossrefs

Cf. A126260, A126261.

Sequence in context: A347555 A215408 A264609 * A330078 A258324 A080499

Adjacent sequences: A126259 A126260 A126261 * A126263 A126264 A126265

Keyword

frac,nonn

Author

Leroy Quet, Dec 22 2006

Extensions

Extended by Ray Chandler, Dec 24 2006

Status

approved