[math-fun] Wilson a^2+b^2-c^2 question
Apparently he intended to ask a question equivalent to the following: Is there a way to express every integer N>=0 in the form a^2 + b^2 - c^2 where a,b,c integers and c^2 <= a^2+b^2 < (c+1)^2 ? An integer S is expressible as a^2+b^2 if and only if its prime divisors of the form 4m+3 have even powers inside S's prime factorization. In particular, every number whose prime factors are 4m+1 primes and the prime 2, only, is thus-expressible. So for example Wilson's question would have a "yes" answer if CONJECTURE: every number N>0 is expressible as 2^k * P - c^2 where P is a prime of form 4m+1, k is in {0,1,2}, and c is integer, and c^2 < 2^k * P < (c+1)^2. Well, what can I say. This conjecture seems extremely likely to be true, in fact I would think every N>0 is thus-expressible in an infinite number of ways. If there were any N only thus-expressible in a finite number of ways, that would be an astonishing find that would win you a Fields medal immediately. But I do not see a way to prove it. Perhaps of some relevance: The ternary form a^2 + b^2 - c^2 is known to represent all integers [Leonard Eugene Dickson: Modern Elementary Theory of Numbers, University of Chicago Press, Chicago, 1939, theorem 109? A.Oppenheim: The determination of all universal ternary quadratic forms, Quart. J. Math. 1 (1930) 179-185] -- Warren D. Smith http://RangeVoting.org <-- add your endorsement (by clicking "endorse" as 1st step)
I crudely piped a prime generator into a Wilson tester. Typical output: 9429 1*22287829 18832 4*22292549 13353 2*22297841 40999 8*52931741 65432 1*1079779313 meaning the number N=9429 is represented as 1*P-floor(sqrt(1*P))^2 where P is a prime of form 4m+1, namely P=22287829. And so on: 18832=4*22292549 - 9442^2, etc. Result: After 7 minutes of printing it had found Wilson/Smith representations for every N={1,2,3,...,65536} in the form N = 2^k * P - c^2 where c = floor(sqrt(2^k * P)) and P=prime of form 4m+1 and k in {0,1,2,3}. Note, previous post I had erroneously said k in {0,1,2} forgetting 3. So this confirms Wilson "yes" conjectured answer out to 2^16, and only primes P below about 2^31 were needed to do it. -- Warren D. Smith http://RangeVoting.org <-- add your endorsement (by clicking "endorse" as 1st step)
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Warren D Smith