The 420 is the next number in a series of numbers that matches numbers commonly used by the

Babylonians, the

60 (60 minutes in an hour), and the

12(12 hours during daylight, 12 starsigns in the

zodiac).

The series is made up by the smallest common multiple of the first n numbers, which is the smallest number that can be divided without a rest by the input numbers.

So

scm(1)=1

scm(1,2)=2

scm(1,2,3)=6

scm(1,2,3,4)=12, not 4*6=24, because 6 is already divisible by 2, 2*6=12 is divisible by 4

scm(1,2,3,4,5)=60

scm(1,2,3,4,5,6)=60, as 60 is already divisible by 6

scm(1,2,3,4,5,6,7)=420

Babylonian mathematics knew fractions, and there were cuneiform symbols for fractions, so one can imagine that the Babylonians liked to have numbers that could be evenly divided. So, they would like the 420.

btw. the smallest common multiple is to the gcd what, in the boolean algebra of logic, is the OR to the AND. However, there's no meaningful negation that would make the smallest common multiple and the gcd part of a boolean algebra.