281 (number)

← 280 281 282 →
← 200 210 220 230 240 250 260 270 280 290 → List of numbers Integers ← 0 100 200 300 400 500 600 700 800 900 →
Cardinal	two hundred eighty-one
Ordinal	281st (two hundred eighty-first)
Factorization	prime
Prime	twin prime
Greek numeral	ΣΠΑ´
Roman numeral	CCLXXXI
Binary	1000110012
Ternary	1011023
Senary	11456
Octal	4318
Duodecimal	1B512
Hexadecimal	11916

281 is the 60th 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.

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 ${\frac {281^{p}-1}{280}}$ is composite for all prime p < 60000.