OFFSET
1,2
LINKS
Robert Israel, Table of n, a(n) for n = 1..103
FORMULA
a(n) = a(n-1) (2^n - 1)/gcd(a(n-1) (2^n-1), (2^n-1) A087689(n-1) + a(n-1)). - Robert Israel, Dec 28 2012
EXAMPLE
a(4)=35 because 1/1 + 1/3 + 1/7 + 1/15 = 54/35.
MAPLE
a:= n -> denom(add(1/(2^i-1), i=1..n)); // Robert Israel, Dec 28 2012
MATHEMATICA
f[n_] := Denominator[Sum[1/(2^i - 1), {i, n}]]; Array[f, 16] (* Robert G. Wilson v, May 25 2011 *)
Denominator[Accumulate[1/(2^Range[20]-1)]] (* Harvey P. Dale, Dec 28 2012 *)
CROSSREFS
KEYWORD
frac,nonn
AUTHOR
Keenan Pepper, Sep 27 2003
EXTENSIONS
More terms from Ray Chandler, Oct 26 2003
STATUS
approved