OFFSET
1,2
COMMENTS
Let x > 0, and let r = (r(k)) be a sequence of positive irrational numbers. Let a(1) be the least positive integer m such that r(1)/m < x, and inductively let a(n) be the least positive integer m such that r(1)/a(1) + ... + r(n-1)/a(n-1) + r(n)/m < x. The sequence (a(n)) is the (r,x)-greedy sequence. We are interested in choices of r and x for which the series r(1)/a(1) + ... + r(n)/a(n) + ... converges to x. See A270744 for a guide to related sequences.
FORMULA
a(n) = ceiling(r(n)/s(n)), where s(n) = 1 - r(1)/a(1) - r(2)/a(2) - ... - r(n-1)/a(n-1).
r(1)/a(1) + ... + r(n)/a(n) + ... = 1
EXAMPLE
a(1) = ceiling(r(1)) = ceiling(1/tau) = ceiling(0.618...) = 1;
a(2) = ceiling(r(2)/(1 - r(1)/1) = 2;
a(3) = ceiling(r(3)/(1 - r(1)/1 - r(2)/2) = 2.
The first 6 terms of the series r(1)/a(1) + ... + r(n)/a(n) + ... are
0.735..., 0.871..., 0.970..., 0.975..., 0.988..., 0.995...
MATHEMATICA
$MaxExtraPrecision = Infinity; z = 19;
r[k_] := N[2/E^k, 1000]; f[x_, 0] = x;
n[x_, k_] := n[x, k] = Ceiling[r[k]/f[x, k - 1]]
f[x_, k_] := f[x, k] = f[x, k - 1] - r[k]/n[x, k]
x = 1; Table[n[x, k], {k, 1, z}]
N[Sum[r[k]/n[x, k], {k, 1, 19}], 200]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Apr 09 2016
STATUS
approved