SEVEN
28 May 2005

"7 more years till the mayan calendar ends..." ~~Steven Waldron 28 May 05



















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Seven is:

"...prime (indivisible by any, save itself and one;I know you know what prime is but I like the way that sounds).

...the fourth prime (one is not prime).

...is odd.

...congruent to 3 mod 4 (there are only two classes of odd primes; those congruent to 1 mod 4 and those 3 mod 4)

...is spelled with 5 letters (one of the nearest two primes to seven) in English and German,

...A number is divisible by seven if and only if the number obtained by doing the following is divisible by seven:
Double the last digit and reduce mod 10. Subtract this number from the rest of the digits (taken as a number).
This test is much more complicated than most.

...the number of dimensions of one of Milnor's exotic spheres.

...is the number of letters in the spelling of the name of god (one name and one spelling, really)in the Hebrew tradition and is thus sacred.

...is the number of complete fingers of my 8th grade shop teacher ("There are seven things you need to remember in shop class...")

...seems to be the upper limit to the number of things a human can reflexively keep track of if they are moving (attackers, prey).

...seems to be the limit to the number of digits that one can store really easily for many people
(that's one reason why the switch to 10 digit phone numbers is problematic).

...the number of "deadly sins" in common practice.

...half the number of needed elementary particles.

...the number of seas, by old reckoning.

Seven is the number of wonders of the ancient world.


That's about all that springs to mind.
People seem to have a bit of a predeliction for seven.

Now a weird one is 28 (a multiple of seven).
It's "perfect"; it is the sum of its own proper divisors.
It's also the last perfect number any of us will see agewise.
The next is 496.

That was fun.

the honorable mathematician
~Kevin Manley
May 05



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Tracy Hicks
223 North Shore
Dallas, TX
75216-1030


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