Doesn't anybody do the following anymore?
An interesting property of the number 91:
Subtracting 91 from a number causes the tens digit to go up by 1, while the units and hundreds digits step down. For example, starting with 336, we get 245, 154, and then 63. Since 91 is 7 times 13, these steps leave unchanged whether the resulting number is divisible by 7 or 13. So this reduction provides a convenient simultaneous divisibility-check for the divisors 7 and 13, which are notoriously hard to do arithmetic with.
If the number is more than 3 digits long, it may be necessary to subtract 910 instead of 91 at first: this operates on the thousands, hundreds, and tens digits of the number, as before incrementing the central digit while decrementing its neighbors.
Occasionally it is necessary to actually subtract 91 in the ordinary way, but one should never need to borrow.
An example: 958 -> 867 -> 776 -> 685 -> 594; at this point take away 91 in the ordinary way to get 503, and then 503 -> 412 -> 321 -> 230. This last is the product of the primes 2, 5, and 23, and therefore is not divisible by 7 or 13; hence neither is the starting number 958.
This reply was brought to you by the number 91 and the letter FLOOB.
Gursky @ 46: The Gandalara series by Garrett and Heydron fits your criteria. The actual geographic identity of the desert is the main "mystery" of the series.
I've been trying to come up with nice mathematical properties of 86. So far the best I can do is
86 = 1 + 2^2 + (3^2)^2
(Eighty-six is one plus two-squared plus three-squared-squared).
Maybe other math-geek Lucifices can do better.
Everything here seems spot-on.
But I got a completely unexpected giggle out of "gnu-control". Sure enough, that's what the caveat on the earlier post says. And I am forced to admit that I have not yet made up my mind about gnu control. The Constitution is inexplicably silent on the subject.
The mind-boggling TANG/GNAT pair reminds me of my favorite palindrome:
T. Eliot, top bard, notes putrid tang emanating, is sad. I'd assign it a name: gnat dirt upset on drab pot toilet.
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