Lesson Find a sequence of transformations of a given number to get a desired number

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Find a sequence of transformations of a given number to get a desired number


Problem 1

Starting with a positive integer,  apply the following operations any number of times
and in any order to produce a list of numbers:
    (1)   double the current term, or
    (2)   delete the last digit of the current term.
An example of such a list is  231,  23,  46,  92,  9,  18.
Find a list which starts with  51  and ends in  129.

Solution

I solved this problem with the help of  Artificial  Intelligence.
I asked  Google  AI  OVERVIEW:

    Is it true that for every k-digit positive integer n, 
    there is a power of 2 whose first k digits coincide with the number n.

Below is the  Google  AI  Overview answer.

The statement is true. [1]  

For every k-digit positive integer n, there is a power of two whose first digits coincide with the number n. 
This is a consequence of the fact that log_{10}(2) is an irrational number, which implies that the fractional parts 
of m*log_{10}(2) are uniformly distributed in the interval [0, 1) (by the Kronecker's Approximation Theorem). [1, 2, 3]  


Understanding the condition 

For a positive integer P to be the leading digits of a power of two, say 2^m, it must satisfy the inequality: 
   P times 10^d <= 2^m < (P+1) times 10^d 

for some integer d >= 0. This means 2^m has the same leading digits as P, followed by d more digits. 

Answer: 

The statement is true because any finite sequence of digits can be the leading digits of a power of two. 
This relies on the irrationality of log_{10}(2) and the uniform distribution of the fractional parts of its multiples. [1, 5]  

References

[1] https://www.quora.com/Prove-that-for-any-natural-number-n-there-esists-a-power-of-2-lets-say-2-k-such-that-2-k-in-its-decimal-expression-is-1-followed-by-n-zeros-and-eventually-other-digits-For-example-for-n-2-2-196-works-How-to-prove-it
[2] https://www.antonellaperucca.net/didactics/Powers-of-2.pdf
[3] https://math.stackexchange.com/questions/1370645/using-kroneckers-theorem-can-we-prove-theres-some-power-of-two-yielding-a-numb
[4] https://math.stackexchange.com/questions/328655/proving-prime-p-divides-binompk-for-k-in-1-ldots-p-1
[5] https://www.reddit.com/r/askmath/comments/18o86pr/is_it_true_that_for_any_positive_integer_n_there/


The link to this  Google  AI  response is

https://www.google.com/search?q=Is+this+statement+true%3F+For+every+k-digit+positive+integer+n%2C+there+is+a+power+of+two+whose+first+n+digits+coincide+with+the+number+n.&rlz=1C1CHBF_enUS1071US1071&oq=Is+this+statement+true%3F+For+every+k-digit+positive+integer+n%2C+there+is+a+power+of+two++whose+first+n+digits+coincide+with+the+number+n.&gs_lcrp=EgZjaHJvbWUyBggAEEUYOTIHCAEQIRiPAjIHCAIQIRiPAjIHCAMQIRiPAtIBCTE3OTZqMGoxNagCCLACAfEFNet2ZYDKsLI&sourceid=chrome&ie=UTF-8

of Dec.4, 2025.

Then  I  asked  Google  AI  another question:

    Find the degree of number 2 which starts 129.


Google  AI  answered:  the degree is  110,  and it is first degree of  2  with this property.

Then I checked using  MS  Excel in my computer

    2%5E110 = 1.29807E+33.

Now I can present the desired sequence of operations

51 -> 102 -> 10 -> 1 -> 2 -> 4 -> 8 -> 16 -> 32 -> 64 -> 128 -> . . . . -> 2%5E110 = 1.29807E+33,

which is a 34-digit integer number  1298074214633706907132624082305024,  whose three starting/leading digits are  129.

Notice that I do not state that this sequence is the shortest possible.

I only state that this explicit sequence produces a desired number.

Thus, the problem is solved and the desired sequence of operations is presented explicitly.


//////////////////////////////////////////


Yes,  in my solution  I  used help from  Google  AI  Overview - I explicitly referred to it,
so it is not stealing - it is normal work in contemporary environment.   Thanks to  Google  AI  for help  ( ! )

And it suggests some art asking right questions and interpreting the  AI  answers properly,
as well as organizing pieces and thoughts into a logically coherent text,
which opens new knowledge and provides new material for teaching and learning.


My other additional lessons on  Miscellaneous word problems  (section 3)  in this site are
    - More complicated problems on finding number of elements in finite subsets
    - Solving problems by the Backward method
    - Minimax linear problems to solve MENTALLY based on common sense
    - Solving linear optimization problems without LP-method by reduction to linear function
    - Solving one special linear minimax problem in 100-D space by the Linear Programming method
    - Miscellaneous logical problems
    - Math Olympiad level problem on divisibility numbers
    - Upper class entertainment Math problems for all ages
    - OVERVIEW of my additional lessons on Miscellaneous word problems, section 3


Use this file/link  ALGEBRA-I - YOUR ONLINE TEXTBOOK  to navigate over all topics and lessons of the online textbook  ALGEBRA-I.

Use this file/link  ALGEBRA-II - YOUR ONLINE TEXTBOOK  to navigate over all topics and lessons of the online textbook  ALGEBRA-II.


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