I have a 1978 Motobecane Mirage, been in the family since new. It is all original except the tires / tubes.

I have attached pictures. Serial number appears to be 4181278.

There is another stamped number, looks like 018. There is another number below the serial number that cannot be read in the photo. It is 156216. On the rear wheel axle piece there is a number looks to be LC7.

This is a 23 inch frame bicycle. My sister has two Motobecane bicycles at her house. One is a Mixte from about the same era. I will get those numbers the next time I am there.

Looks like the serial numbers are 7 digits in sequence. The 1978 era ones seem to begin with a 4 (million?).