# 281 (number)

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 ← 280 281 282 →
Cardinaltwo hundred eighty-one
Ordinal281st
(two hundred eighty-first)
Factorizationprime
Primetwin prime
Greek numeralΣΠΑ´
Roman numeralCCLXXXI
Binary1000110012
Ternary1011023
Quaternary101214
Quinary21115
Senary11456
Octal4318
Duodecimal1B512
Hexadecimal11916
VigesimalE120
Base 367T36

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