[seqfan] Re: An equivalence for integer sequences (with more questions than answers)
Giovanni Resta
g.resta at iit.cnr.it
Fri Feb 27 11:57:37 CET 2009
Paolo Lava wrote:
> To avoid “NA” we could consider the terms of the sequence as coefficients of a simple continued fraction. For instance:
>
> a(n) N
> n .6977746580… Positive integers
> 2*n .4463899659… Even numbers
> 2*n-1 .7615941560… Odd numbers
The fact that periodic continued fractions like those
for 1,2,1,2,1,2 or 2,1,2,1,2 lead to numbers
like 0.733 = sqrt(3)-1 and 0.366=(sqrt(3)-1)/2 is well known.
Instead, I was a little surprised (given my immense ignorance...) by
the continued fractions for
1,2,3,4,5,6,... (naturals) -> BesselI(1,2)/BesselI(0,2),
2,4,6,8,10,... (even numbers) -> BesselI(1,1)/BesselI(0,1)
1,3,5,7,9,... (odd numbers) -> tanh(1).
I confess I have no idea of "why" (I used the Inverse Symb. Calc.
to spot the identities and Mathematica to check them (numerically)
up to 50 digits.
giovanni
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