| ||||
|---|---|---|---|---|
| Cardinal | two hundred eighty-one | |||
| Ordinal | 281st (two hundred eighty-first) | |||
| Factorization | prime | |||
| Prime | 60th | |||
| Greek numeral | ΣΠΑ´ | |||
| Roman numeral | CCLXXXI | |||
| Binary | 1000110012 | |||
| Ternary | 1011023 | |||
| Senary | 11456 | |||
| Octal | 4318 | |||
| Duodecimal | 1B512 | |||
| Hexadecimal | 11916 | |||
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 is composite for all prime p < 60000.
References
- ↑ Sloane, N. J. A. (ed.). "Sequence A001359 (Lesser of twin primes)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
- ↑ Sloane, N. J. A. (ed.). "Sequence A005384 (Sophie Germain primes p: 2p+1 is also prime)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
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