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420 (four hundred [and] twenty) is the natural number following 419 and preceding 421.
In mathematics
420 is:
- the sum of four consecutive primes ().
- the sum of the first twenty positive even numbers.
- a zero of the Mertens function[1] and is sparsely totient.[2]
- a pronic number.[3]
- 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.[4]
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.
References
- ^ "Sloane's A028442 : Numbers n such that Mertens' function is zero". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-06-02.
- ^ "Sloane's A036913 : Sparsely totient numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-06-02.
- ^ "Sloane's A002378 : Oblong (or promic, pronic, or heteromecic) numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-06-02.
- ^ Sloane, N. J. A. (ed.). "Sequence A020492 (Balanced numbers: numbers k such that phi(k) (A000010) divides sigma(k) (A000203))". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
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