Re: prime numbers and African artifact
Peter Seebach (seebs@solutions.solon.com)
13 Jul 1995 15:45:20 0500
In article <3u0rjh$g2g@zen.hursley.ibm.com>,
Martin Bright <mbright@vnet.ibm.com> wrote:
>Peter Seebach (seebs@solutions.solon.com) wrote:
>> > What's the easy way to show that 254365465431652436514232 is not
>> >prime again?
> Simple!
>> 2 + 5 + 4 + 3 + 6 + 5 + 4 + 6 + 5 + 4 + 3 + 1 +
>> 6 + 5 + 2 + 4 + 3 + 6 + 5 + 1 + 4 + 2 + 3 + 2 = 91
>> 9 + 1 = 10.
>> 1 + 0 = 1.
>> 1 is not a multiple of three, so the whole number is not a multiple of
>> three, so it must be prime!
>Also the first two digits aren't divisible by 4, so the whole number isn't
>divisible by 4. This proves again that it is prime.
Actually, this is incorrect. If the *last* two digits are divisible by 4, the
whole number is divisible by 4. However, since they aren't (they're 3 and 2),
the number isn't divisible by four. (The way this works is, since it's not a
multiple of four or a multiple of three, it's not a multiple of (4 * 3), so
it's not a multiple of 12  like 13, which is also prime.
s

Peter Seebach  seebs@solon.com  seebs@intran.xerox.com
All the arrogant jerks who object to stereotypes are all alike.
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Copyright 1995 Peter Seebach. Not for distribution through Microsoft Network.
