[Edu-sig] Mystery Number 6174
Scott David Daniels
Scott.Daniels at Acm.Org
Sun Jul 6 22:54:34 CEST 2008
kirby urner wrote:
> Yutaka Nishiyama has this interesting article in the March 2006 issue
> of Plus, entitled 'Mysterious number 6174'.
>
> The theorem in this article is as follows: any 4-digit positive
> integer, stipulating all 4 digits *not* be the same one, may be
> distilled to 6174 by the following
> process: extract the largest and smallest two integers from the 4
> digits and subtract the smaller from the larger, and repeat as
> necessary.
...
> Here's one way to test the result. Think of a different way?
def counts(limit=7, closer=6174):
counts = [0] * limit
exceptions = set()
for ournum in range(10000):
start = quad = ''.join(sorted('%04d' % ournum))
if quad[0] == quad[3] or quad in exceptions:
continue
for distance in range(limit):
diff = int(''.join(reversed(quad))) - int(quad)
if diff == closer:
break
quad = ''.join(sorted('%04d' % diff))
else:
exceptions.add(start)
counts[distance] += 1
return counts, sorted(exceptions)
-Scott
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