281 (number)

← 280 281 282 →
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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
Quaternary 101214
Quinary 21115
Senary 11456
Octal 4318
Duodecimal 1B512
Hexadecimal 11916
Vigesimal E120
Base 36 7T36

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 is composite for all prime p < 60000.


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