281 (number) explained

Number:	281
Prime:	60th

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,^[1] Sophie Germain prime,^[2] 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

(281 ^{p-1})/(280) is composite for all prime p < 60000.

Notes and References

1. Lesser of twin primes.
2. Sophie Germain primes p: 2p+1 is also prime.