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PROJECT EULER · #0420

2×2 Positive Integer Matrix

Statement only · UnsolvedOriginal problem ↗

A positive integer matrix is a matrix whose elements are all positive integers.
Some positive integer matrices can be expressed as a square of a positive integer matrix in two different ways. Here is an example:

(40124840)=(23122)2=(6146)2

We define F(N) as the number of the 2×2 positive integer matrices which have a tracethe sum of the elements on the main diagonal less than N and which can be expressed as a square of a positive integer matrix in two different ways.
We can verify that F(50)=7 and F(1000)=1019.

Find F(107).

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