How many to hang in pixels?

Marketing is the imposition of an unnecessary product by artificially creating a non-existent need for it. Looking at the aggressiveness with which cameraphones appear, I decided to find out how much megapixels actually need an ordinary person.

Original data: 300 pixels / inch, standard sizes for photo printing. So, let's go:

Print size	Image size	Number of pixels	Mhr *
10.2 x 15.2	1205 x 1796	2 164 180	3
15.2 x 21.6	1796 x 2552	4,583,392	five
20.3 x 30.5	2398 x 3603	8,639,994	9
30.5 x 45.7	3603 x 5398	19,448,994	20

You do not agree?
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* - rounding to integer.