perplexus.info :: Numbers : Squares built from leftovers

Squares built from leftovers (Posted on 2018-04-05)

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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