* A square such that area of inner region A equals area of region B: __________________ | : | | : | | : | | A : | | : | | : | |.............: | | B | |__________________| Also, what about "rings" such that the area of A equals that of B (see below)? This would extend better to other shapes, such as circles. Yeah, try circles first. Wait a minute, the answer ought to be obvious... oh, duh, it's just when one circumference is twice as long as the other, since they're just multiplied by a constant pi. But the same is not true of the other shapes, aha! __________________ | ,............, | | : : | | : : | | : A : | | : : | | : : | |B :............: | |__________________| * (N + 1)^2 = N^2 + 2N + 1 and (N + 1)^3 = N^3 + (N + 1)^2 + 2N^2 + N Visualize a square, then a cube, to see why. Now go on to hypercube, then n-cubes. * The number of N's divisors is equal to the number of unique multiplicative combinations of its unique prime factors? Let's see: Instead of generating primes, how about generating composites and taking the holes? * Some thoughts: Def: Sum-Pfactrs(N) = the sum of its prime factorization Def: Choiceness(N) = N / Sum-Pfactrs(N) Or maybe choiceness is more appropriately the number of prime factors (with 1 being highest grade of choice, also called prime), or maybe unique prime factors, or... How does Sum-Pfactrs(N) compare with the sum N's divisors... compare with the sum of [1...N]? * Are there any odd perfect numbers? A perfect number is the sum of its divisors, including 1 but not including itself. For example: 6 = 1 + 2 + 3. Thoughts: well, let's take a look at divisors of odd and even numbers, and see if we can't find some pattern. Then see if the pattern admits of proof? Each divisor D1 of a number N has a "partner" D2, such that (D1 * D2 = N), right? Here are two parity tables, where E means even and O means odd: (D1 * D2 = N) (D1 + D2 = N) _________________ _________________ |N D1 D2 | |N D1 D2 | |-----------------| |-----------------| |E E O/E | |E E E | | O E | | O O | |.................| |.................| |O E ? | |O E O | | O O | | O E | |_________________| |_________________| The only ambiguity is in the first table; if N and D1 are both even, then D2 can be even or odd, and if N is odd, then neither D1 nor D2 can be even. Forgetting about the 1, since it's a constant component anyway, we know that any number N has an even number of divisors, because each divisor D1 must have its counterpart D2. No D1 could have two or more different counterparts, for (N / D1) must always equal the same number. So what would it mean for an odd number N to be perfect? Well, it would mean that an even number of divisors had summed up to an even number (remember, it will be odd once we add the 1 back on). If X of those divisors are odd, then X must be even, for N to be even as well. By definition, all the other divisors of N are even numbers, if they exist at all. This means that an even number of even numbers has been added to an even number of odd numbers, to produce an even number. Then 1 is added, to produce an odd number. All well and good, no contradictions so far. Now let's multiply them out instead of adding. We should obtain the same N, but we can really forget about the 1 this time. If N is to be odd, then it can have no even divisors at all (it only takes one of them to "contaminate" the product). It follows that all the divisors of N must be odd, and there must be an even number of them. This leads to the first requirement for an odd perfect number N: Req. 1: All divisors of N are odd. This could have been arrived at much more simply, by noting that any even divisors at all would lead to an even N. Sigh. IDEA: wait!!! There is one thing about even Ns -- they all, without fail, have 2 as a divisor. There is no such required number for odd Ns -- any old collection of odd numbers willl do. Hmm... can a contradiction be shown in having your divisors sum up to yourself if they are all greater than 2 (except for the 1)? Seems the most promising way to go. * Hey, there's always Goldbach's conjecture. :-)