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Squares built from leftovers (Posted on 2018-04-05) Difficulty: 2 of 5
Let N1=123456789
Erase n digits and shrink the remnants of N1 into one continuous chain creating a new number N1'.

What is the minimum number of digits to be erased so that N1' will be a square number?

Same question for N2=987654321 and N2'.

See The Solution Submitted by Ady TZIDON    
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Solution by cheating | Comment 2 of 4 |
If you consider looking up the numbers on OEIS to be cheating.
I found the numbers up to 3 digits then searched and found
http://oeis.org/A122683
The largest number is 134689, three digits erased

http://oeis.org/A124683
The largest number is 961, six digits erased. 
(I'm surprised at having to erase so many.) 

Edited on April 5, 2018, 2:54 pm
  Posted by Jer on 2018-04-05 14:33:51

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