4K resolution
As noted above, DCI 4K is 40962160, while 4K UHD is 38402160, producing a slight difference in aspect ratio rather than a significant difference in resolution. Traditional displays, such as LCD or OLED, are 3840 pixels across the screen, with each pixel being 1/3840th of the screen width. They do not overlap—if they did, they would suffer reduced detail. The diameter of each pixel is basically 1/3840th of the screen width or 1/2160th of the screen height - either gives the same size pixel. That 38402160 works out to 8.3 megapixels, the official resolution of 4K UHD (and therefore Blu-ray UHD discs).
16K resolution
The term 16K resolution (8640p) refers to a display resolution that has 15360 horizontal pixels by 8640 vertical pixels, for a total of 132.7 megapixels. It has four times as many pixels as 8K resolution, sixteen times as many pixels as 4K resolution and sixty-four times as many pixels as 1080p resolution.