stigant wrote:
That's not the point... the condition I gave for 17 and 19 IS a positive definition (ie when you multiply their last digit by 4, you get the first two digits of their square), and 13 fails it.
I'm not arguing with that, it is correct. The point is, the numbers 1, 2 and 3 fail it too
stigant wrote:
For that matter, being prime could be (and usually IS) stated negatively: Any number that does not have divisors other than itself and 1. Whereas being composite is stated positively: HAS divisors other than itself and 1.
This is correct too. But while the primes group is a complement of the composites group and vice versa, "
primes"
are a known and acknowledged group mentioned countless times, including in this thread. "
Non-squares"
however is clearly a group defined as a complement. If you will be asked what features the number 13 has, "
prime"
would be among the first you will come out with, and I seriously doubt "
non-square"
will be mentioned at all.
That's why Schik deserves a point for answering "
2 is even"
even if it's not what I had in mind (people are too attached to the "
odd"
and "
even"
groups), and Hix doesn't deserve a point for answering "
1 is the only square"
.
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