400 (number)

Encyclopedia : 4 : 40 : 400 : 400 (number)

Four hundred is the natural number following three hundred [and] ninety-nine and preceding four hundred [and] one.

List of numbers — Integers

<< 0 100 200 300 400 500 600 700 800 900 >>

Cardinal Four hundred
Ordinal 400th
Factorization [2^4 \cdot 5^2]
Roman numeral CD
Binary 110010000
Duodecimal 294
Hexadecimal 190
Vigesimal 100
Hebrew ת (Tav)

Mathematical properties

400 is the square of 20.

A circle is divided into 400 grads, which is equal to 360 degrees and 2π radians. (Degrees and radians are the SI accepted units).

400 is a self number in base 10, since there is no integer that added to the sum of its own digits results in 400. On the other hand, 400 is divisible by the sum of its own base 10 digits, making it a Harshad number.

Other fields

Four hundred is also

an HTTP status code for a bad request.
a phrase meaning the wealthiest, most famous, or most powerful social group, leading to the generation of such lists as the Forbes 400
The Atari 400 home computer.
in the title of the film Les Quatre Cent Coups (The 400 Blows), a French film directed by François Truffaut.
the designation for a class of Ontario highways called 400-Series Highways.

For the year 400 AD, see 400.

Integers from 401 to 499

401 prime number, tetranacci number, sum of seven consecutive primes (43 + 47 + 53 + 59 + 61 + 67 + 71), sum of nine consecutive primes (29 + 31 + 37 + 41 + 43 + 47 + 53 + 59 + 61), Chen prime, Eisenstein prime with no imaginary part, Mertens function returns 0. Also, area code for Rhode Island, also HTTP status code for an unauthorized request, also in the name of a retirement plan, 401(k)

402 = 2 × 3 × 67, sphenic number, nontotient, Harshad number, also HTTP status code for payment required

403 = 13 × 31, Mertens function returns 0. Also, HTTP status code for forbidden, also in the name of a retirement plan, 403(b)

404 = 2² × 101, Mertens function returns 0, nontotient, noncototient. Also, HTTP status code for "file not found", perhaps the most famous HTTP status code of all time.

405 = 3⁴ × 5, Mertens function returns 0, Harshad number; HTTP error code for "Method not allowed"; see also Interstate 405

406 = 2 × 7 × 29, sphenic number, triangular number, centered nonagonal number, nontotient, untouchable number, also area code for Montana, and HTTP error code for "Not acceptable".

is a poem by John Boyle O'Reilly. It was believed to have been the number of one of O'Reilly's prison cells, and was the number of his first hotel room after he arrived in the United States. Hence the number had a mystical significance to him, as intimated in the poem.