420 (number)

420 (four hundred [and] twenty) is the natural number following 419 and preceding 421.

In mathematics
420 is:
 * the sum of four consecutive primes ($$101+103+107+109$$).
 * the sum of the first twenty positive even numbers.
 * a zero of the Mertens function and is sparsely totient.
 * a pronic number.
 * the smallest number divisible by the numbers from 1 to 7; as a consequence of that, it is a Harshad number in bases 2 to 10, except in base 5.
 * a 141-gonal number.
 * a balanced number.

In other fields

 * 420 is a slang term that refers to the consumption of cannabis. April 20th is commonly celebrated as a holiday dedicated to the drug, due the day being notated as 4/20 in the month-day-year format. Because of these associations, 420 has been humorously referred to as the "weed number". "Weed" is a slang term for cannabis.
 * 420 is the country calling code for Czech Republic.