According the Phil Askey's review, the sensor has 5.33 million pixels. There is often a disparity between the total number of pixels on a given sensor, and the number of pixels that are actually used for image capture. Either the designers choose to limit the pixels used or the edge pixels are factored out to preserve edge quality.
With the D1x there's an additional complication. The horizontal resolution of the sensor is double the vertical resolution. The camera creates 5.88 Mpix images using interpolation to fill in the vertical data.