Given the look and say sequence with a seed of 1,
Is it true that this is a strictly increasing sequence?
Notes:
The sequence is in base . To prove for a general base may be extremely difficult
This may help: Cosmological Theorem
This may also help: Look and Say Sequence
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Sorry about the sloppy writing, there was just too much to write about. I hope it serves as a general idea.
Facts:
1- there can only be runs of length 3 or less of any digit, because of the nature of the dynamical rule. To understand, if we have 2 2 2 2 as part of the element a n of the sequence, it means that the corresponding part in a n − 1 has been 2 2 2 2 , which should be translate into 4 2 rather than 2 2 2 2 .
As a consequence digits of the elements of the sequence can only be { 1 , 2 , 3 } , given the seed is 1 .
2- If we index the digits of a number as a 0 a 1 … a t , then a run of length 3 can only start at an even position.
3- runs of length 1 , 2 , 3 in a n would cause the following number digits in a n + 1 : 2 , 2 , 2 .
4- No element a n would start with a run of length 2 or 3 of the digits 2 or 3 . Because, if there is such an element, going backwards in the sequence, we would always have elements that would start with 2 or 3 , but obviously the seed is 1 (starts with 1).
Now we put facts together. If a n consists of only runs of length 1, the obviously a n < a n + 1 .
If a n consists of both runs of length 1 and 2 and no run of length 3, then the number of digits of a n + 1 is more than the number of digits a n , hence a n < a n + 1 .
If a n consists only of runs of length 2,the length is maintained, but it should start with 1 1 which leads to a n + 1 starting with 2 1 , so a n < a n + 1 .
If a n contains any run of length 3, then it would be followed by a run of length 1 , which automatically compensate the reduction of the number of digits in a n + 1 that is caused by the run of length 3 . So, the number of digits of a n + 1 would not be less than the number of digits of a n . Now, in case a n and a n + 1 have the same number of digits, if a n starts with 1 1 , then a n < a n + 1 , for a n + 1 start with 2 1 . Note that if it starts with a run of 1 , then the number of digits of a n + 1 would be definitely more than the number digits of a n .