perplexus.info :: Just Math : Reverse Rigor II

Reverse Rigor II (Posted on 2014-07-22)

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.

See The Solution Submitted by K Sengupta

Rating: 5.0000 (1 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)

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

the GCD comes out as 99.

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

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