Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A problem in Pythagorean Arithmetic   Problem 2 at the 56th International Mathematical Olympiad (2015) asks for all
triples (a,b,c) of positive integers for which ab-c, bc-a, and ca-b are all
powers of 2. We show that this problem requires only a primitive form of
arithmetic, going back to the Pythagoreans, which is the arithmetic of the even
and the odd.

28
The categories of this paper are: alg-geom
21
The categories of this paper are: adap-org
13
The categories of this paper are: quant-ph
29
The categories of this paper are: funct-an
23
The categories of this paper are: solv-int
36
The categories of this paper are: cmp-lg
8
The categories of this paper are: hep-ex
12
The categories of this paper are: nucl-th
18
The categories of this paper are: econ
35
The categories of this paper are: mtrl-th
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The categories of this paper are: comp-gas
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The categories of this paper are: bayes-an
37
The categories of this paper are: supr-con
9
The categories of this paper are: nlin
24
The categories of this paper are: dg-ga
6
The categories of this paper are: astro-ph