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My own way was Alison's method.
I found 10 different ways you can make the general army hollow squares.
A formula for finding the different ways the general could organize his army, is dividing his army into 4 equal parts like Alison's formula, then you find all the ways that you could find the area of each of the 4 parts. In the general's army there are 960 troops you then break it into the 4 parts, then each of those parts is 240 and then you all the different products that equal 240 making up each of the parts.
The 10 different ways for the general's army are:
[1x240]x4
[2x120]x4
[3x80]x4
[4x60]x4
[5x48]x4
[6x40]x4
[8x30]x4
[10x24]x4
[12x20]x4
[15x16]x4