I was contemplating convergent sums, trying to think of very unusual or unorthodox sums that might be treatable recursively. Eventually, the following sum occurred to me:
ξ=1+12+34+78+⋯⋯89+⋯⋯45+910+⋯⋯1011+⋯⋯23+56+1112+⋯⋯1213+⋯⋯67+1314+⋯⋯1415+⋯⋯⋯
There is no especial motivation, but I endeavored to determine if I could show at least that it was bounded. I was not sure how to treat it however; it seemed like it might be possible to put it into some form of continued fraction, however I confess I am not familiar enough with continued fractions to see how this might be done (if it is possible). I calculated the first "convergents", or terms of the sequence {ξn}n∈N0 as I imagined it, if I were to write it as
ξ0=1,ξ1=1+1223=1+34=1.75,ξ2=1+12+344523+5667=1+12+151623+3536=1+23165936≈1.87712,ξ3=1+12+34+788945+910101123+56+1112121367+13141415=⋯≈1.8887.
which reinforced my thought that it was potentially a convergent sum. If anyone has any advice as to what methods may be used to establish this, or any other insights, they would be a great assistance in sating my curiosity.
The perceived intractability of the aforementioned sum lead me to consider the "visually similar" but more simple sum
1+1223+34455667+788991010111112121313141415+⋯
One can notice that the fraction ratios are of the form p−1ppp+1=p2−1p2=1−1p2, so that I could express this sum as
1+(1−122)+1−1421−162+(1−182)(1−1142)(1−1102)(1−1122)+(1−1162)(1−1222)(1−1262)(1−1282)(1−1182)(1−1202)(1−1242)(1−1302)+⋯
Unfortunately, I do not see a very obvious way to generalize this to a sum perhaps roughly of the form
∑n∈2Z+2n∏i=0( something... )
which might be tackled more effectively.
If anyone can offer any assistance, or is familiar with similar problems, I am very interested in learning more regarding properties, especially convergence, of these types of "nested" sums.
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