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 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.

 No Solution Yet Submitted by K Sengupta No Rating

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 possible computer solution | Comment 1 of 4
DefDbl A-Z
Dim crlf\$, sofar

ChDir "C:\Program Files (x86)\DevStudio\VB\projects\flooble"
Text1.Text = ""
crlf\$ = Chr(13) + Chr(10)
Form1.Visible = True
DoEvents

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

Text1.Text = Text1.Text & crlf & "done"
End Sub

Function reverse(n)
s\$ = LTrim(Str(n))
v = 0
For i = Len(s\$) To 1 Step -1
v = 10 * v + Val(Mid(s\$, i, 1))
Next
reverse = v
End Function

Function gcd(a, b)
x = a: y = b
Do
q = Int(x / y)
z = x - q * y
x = y: y = z
Loop Until z = 0
gcd = x
End Function

finds the GCD among the formulas coming from all N tested as 9.

 Posted by Charlie on 2014-07-22 11:58:31

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