Leica M Typ 240 has a
24.0MP Full frame (36 x 24 mm ) sized CMOS sensor . On the other hand, Nikon P510 has a
16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features Expeed C2 processor.
Leica M Typ 240's sensor provides 8MP more than Nikon P510's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the M Typ 240 and P510 sensor size comparison.
As seen above, Leica M Typ 240 has a 30.8x Larger sensor area than Nikon P510. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.