How Boeings are named?

I know many people have their own definite perspective regarding this query. Some do believe that it's because 7 is the lucky numbers. Some of the mathematicians take it differently.  But, the actual thing is quite different.

 After the declaration of the end of the World War II, a move was originated by the Boeing company for the manufacture of passenger carrying planes for a commercial purpose aside military air crafts.
At the following time, every sector was provided with various number codes. The number was distributed as follow.
300s and 400s for the military sector
500s for the turbine engines
600s for rockets and missiles
700s for transport  plane

The 707 was finally the introduced as the passenger carrying commercial Boeing back in October 1958. The following achievement was regarded as the commencement of the"Jet Era".It was announced that any 3 digit number starting and ending with 7 will be the commercial aircraft.Later on, Boeing 727, 737, 747,757, 767,777,717, 787. Besides, Boeing 707 all 7✕7 series are operative till date. The jumbo jet 747 was regarded as the largest aircraft of the era. The design of the 1960s firstly developed 747 consists of the wing spread largely as the basketball court.