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Reverse Rigor II (Posted on 2014-07-22) Difficulty: 3 of 5
Denote by R(N) the integer obtained by reversing the digits of a positive integer N.

Determine the largest integer that is certain to divide N4 - (R(N))4, with N > R(N), regardless of the choice of N.

No Solution Yet Submitted by K Sengupta    
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Solution re(2): possible computer solution Comment 4 of 4 |
(In reply to re: possible computer solution by Ady TZIDON)

You are absolutely correct.


With

 For n = 10 To 10000
  rn = reverse(n)
  If n > rn Then
   If flag = 0 Then
    sofar = n * n * n * n - rn * rn * rn * rn
    flag = 1
   Else
    sofar = gcd(sofar, n * n * n * n - rn * rn * rn * rn)
   End If
   Text1.Text = Text1.Text & Str(n) & Str(rn) & Str(sofar) & crlf
   DoEvents
  End If
 Next

the GCD comes out as 99.

  Posted by Charlie on 2014-07-22 13:43:14
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