 |
|
| Science Forum Index » Mathematics Forum » Reverse Look and Say Sequence... |
|
Page 1 of 1 |
|
| Author |
Message |
| Jim Ferry... |
 Posted: Fri Nov 06, 2009 10:32 am |
|
|
|
Guest
|
Consider the following sequence
1
11
12
2111
1321
11213111
1331112112
211221133211
where each line is formed by "look and say" from the
previous, and then reversed. (See
http://en.wikipedia.org/wiki/Look-and-say_sequence
for the standard look-and-say sequence.)
This sequence is A022481 in Sloane. (Equivalently,
and perhaps more naturally, the sequence of the
reverses of the above is A006711).
The lengths of these strings is A022476 in Sloane:
1, 2, 2, 4, 4, 8, 10, 12, 14, 20, 24, 30, 38, 54, 66, 92,
120, 160, 210, 284, 378, 490, 632, 852, 1134, ....
Whereas the asymptotic growth rate of the standard
look-and-say sequence is
1.303577269034296391257...
(an algebraic integer of degree 71), numerical
experimentation indicates the asymptotic growth
rate of the reverse sequence is approximately
1.327.
As in the standard case, this growth rate is
independent of the initial condition.
Is anyone aware of an analysis of this reverse
case? E.g., what are the "elements" and what
is the minimal polynomial for the asymptotic
growth rate?
I computed 56 terms before running out of
memory in Mathematica, which was not
enough to find a linear recurrence (which
would yield the minimal polynomial). |
|
|
| Back to top |
|
|
|
| Jim Ferry... |
| Posted: Sat Nov 07, 2009 3:40 pm |
|
|
|
Guest
|
On Nov 6, 3:32 pm, Jim Ferry <corkleb... at (no spam) hotmail.com> wrote:
[quote]Consider the following sequence
1
11
12
2111
1321
11213111
1331112112
211221133211
where each line is formed by "look and say" from the
previous, and then reversed. (Seehttp://en.wikipedia.org/wiki/Look-and-say_sequence
for the standard look-and-say sequence.)
This sequence is A022481 in Sloane. (Equivalently,
and perhaps more naturally, the sequence of the
reverses of the above is A006711).
The lengths of these strings is A022476 in Sloane:
1, 2, 2, 4, 4, 8, 10, 12, 14, 20, 24, 30, 38, 54, 66, 92,
120, 160, 210, 284, 378, 490, 632, 852, 1134, ....
Whereas the asymptotic growth rate of the standard
look-and-say sequence is
1.303577269034296391257...
(an algebraic integer of degree 71), numerical
experimentation indicates the asymptotic growth
rate of the reverse sequence is approximately
1.327.
As in the standard case, this growth rate is
independent of the initial condition.
Is anyone aware of an analysis of this reverse
case? E.g., what are the "elements" and what
is the minimal polynomial for the asymptotic
growth rate?
I computed 56 terms before running out of
memory in Mathematica, which was not
enough to find a linear recurrence (which
would yield the minimal polynomial).
[/quote]
I forgot to mention that a Maple user could
probably figure this out without much effort
using Ekhad's and Zeilberger's package HORTON:
http://www.math.rutgers.edu/~zeilberg/mamarim/mamarimhtml/horton.html
Unfortunately, I'm an adherent of another
denomination (the one with the infallible
supreme leader). |
|
|
| Back to top |
|
|
|
| cbrown at (no spam) cbrownsystems.com... |
| Posted: Sat Nov 07, 2009 8:04 pm |
|
|
|
Guest
|
On Nov 6, 12:32 pm, Jim Ferry <corkleb... at (no spam) hotmail.com> wrote:
[quote]Consider the following sequence
1
11
12
2111
1321
11213111
1331112112
211221133211
where each line is formed by "look and say" from the
previous, and then reversed. (Seehttp://en.wikipedia.org/wiki/Look-and-say_sequence
for the standard look-and-say sequence.)
This sequence is A022481 in Sloane. (Equivalently,
and perhaps more naturally, the sequence of the
reverses of the above is A006711).
[/quote]
I think it disappointing that the reverses do not have Sloan sequence
number 184220A  . Or at least A101122031405060718.
Cheers - Chas |
|
|
| Back to top |
|
|
|
|
|
All times are GMT - 5 Hours
The time now is Mon Dec 07, 2009 5:19 pm
|
|