281 (number)

281 is the natural number following 280 and preceding 282. It is also a prime number.

In mathematics

281 is a 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, and a centered decagonal number.

281 is the smallest prime p such that the decimal period length of the reciprocal of p is (p−1)/10, i.e. the period length of 1/281 is 28. However, in binary, it has period length 70.

The generalized repunit number ${\displaystyle {\frac {281^{p}-1}{280}}}$ is composite for all prime p < 60000.

References