289 (number)

280

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List of numbers — Integers

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two hundred eighty

280th
(two hundred eightieth)

2³× 5 × 7

CCLXXX

100011000₂

101101₃

10120₄

2110₅

1144₆

430₈

1B4₁₂

118₁₆

E0₂₀

7S₃₆

280 (two hundred [and] eighty) is the natural number after 279 and before 281.

The denominator of the eighth harmonic number, 280 is an octagonal number.

There are 280 plane trees with ten nodes. As a consequence of this, 18 people around a round table can shake hands with each other in non-crossing ways, in 280 different ways (this includes rotations).

280 is a base 10 Harshad number.

See also the year 280.

Two hundred [and] eighty-one 281 prime, twin prime with 283, Sophie Germain prime, sum of the first fourteen primes, sum of seven consecutive primes (29 + 31 + 37 + 41 + 43 + 47 + 53), Chen prime, Eisenstein prime with no imaginary part, centered decagonal number

Two hundred [and] eighty-two 282 = 2·3·47, sphenic number

Two hundred [and] eighty-three 283 prime, twin prime with 281, strictly non-palindromic number

Two hundred [and] eighty-four 284= 2·2·71, amicable number with 220; nontotient. 284 degrees Celsius is the flash point of paper.

Two hundred [and] eighty-five 285 = 3·5·19, sphenic number, square pyramidal number, Harshad number, also in Star Trek, the total number of Rules of Acquisition, repdigit in base 7 (555).

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