OFFSET
1,2
COMMENTS
R. K. Guy observes (Nov 23 2005) that it appears that f(n) is an integer iff n = 1, 3, 8, 9, when f(n) = 1, 2, 18, 26 respectively.
EXAMPLE
1, 3/2, 2, 7/2, 21/5, 42/5, 48/5, 18, 26, 234/5, 2808/55, 6552/55, 7056/55, 12096/55, 96768/275, 187488/275, 3374784/4675, 7312032/4675, 29248128/17765, 307105344/88825, ...
MAPLE
with(numtheory); f:=n->mul(sigma(i)/i, i=1..n);
MATHEMATICA
f[n_] := Denominator@ Product[ DivisorSigma[1, i]/i, {i, n}]; Array[f, 36] (* Robert G. Wilson v, May 01 2006 *)
Denominator[Rest[FoldList[Times, 1, Table[DivisorSigma[1, i]/i, {i, 40}]]]] (* Harvey P. Dale, Nov 12 2014 *)
CROSSREFS
KEYWORD
nonn,frac
AUTHOR
N. J. A. Sloane, Nov 27 2005
STATUS
approved