Continued fractions as inverted recurrence relations
Joseph Biberstine
jrbibers at indiana.edu
Tue May 2 23:17:57 CEST 2006
As in http://functions.wolfram.com/Constants/Pi/10/0006/, we see the
following:
4/Pi = 1 + 1/(3 + 4/(5 + 9/(7 + 16/(9 + 25/(11 + ...))))) that is, this
is a non-simple cont.frac. where the numerators are the squares and the
partial quotients are the odds.
Consider a[n] = 2*n - 1 + n^2/a[n+1] with a[1] = 4/Pi.
Solving the above recurrence in the other direction we would have a[n] =
(n-1)^2/(a[n-1 - 2*n + 3) with a[1] = 4/Pi.
Now consider this last defined sequence a[n]. We suspect it grows
linearly, (1) does it? (2) What is the limit of a[n]/n as n->Infinity?
If this limit exists, (3) is it in the OEIS and (4) can it be
expressed in closed form? We suspect the value of a[1] is largely
inconsequential, (5) is it? If this limit exists, (6) how if at all
does it relate to Pi?
If the limit does exist, it appear to be approximately 0.414 (roughly
a[2000]/2000), though I have no means to calculate it further.
- J. Biberstine
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