281 (number)

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← 280 281 282 →
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.

Related Research Articles

2 (two) is a number, numeral and digit. It is the natural number following 1 and preceding 3. It is the smallest and only even prime number. Because it forms the basis of a duality, it has religious and spiritual significance in many cultures.

1000 or one thousand is the natural number following 999 and preceding 1001. In most English-speaking countries, it can be written with or without a comma or sometimes a period separating the thousands digit: 1,000.

400 is the natural number following 399 and preceding 401.

500 is the natural number following 499 and preceding 501.

700 is the natural number following 699 and preceding 701.

600 is the natural number following 599 and preceding 601.

800 is the natural number following 799 and preceding 801.

900 is the natural number following 899 and preceding 901. It is the square of 30 and the sum of Euler's totient function for the first 54 positive integers. In base 10 it is a Harshad number. It is also the first number to be the square of a sphenic number.

2000 is a natural number following 1999 and preceding 2001.

3000 is the natural number following 2999 and preceding 3001. It is the smallest number requiring thirteen letters in English.

4000 is the natural number following 3999 and preceding 4001. It is a decagonal number.

5000 is the natural number following 4999 and preceding 5001. Five thousand is the largest isogrammic numeral in the English language.

6000 is the natural number following 5999 and preceding 6001.

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227 is the natural number between 226 and 228. It is also a prime number.

233 is the natural number following 232 and preceding 234.

251 is the natural number between 250 and 252. It is also a prime number.

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References

  1. ↑ Sloane, N. J. A. (ed.). "SequenceA001359(Lesser of twin primes)". The On-Line Encyclopedia of Integer Sequences . OEIS Foundation.
  2. ↑ Sloane, N. J. A. (ed.). "SequenceA005384(Sophie Germain primes p: 2p+1 is also prime)". The On-Line Encyclopedia of Integer Sequences . OEIS Foundation.
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