# 261 (number)

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Cardinal | two hundred sixty-one | |||

Ordinal |
261st (two hundred sixty-first) | |||

Factorization |
3^{2}× 29 | |||

Divisors | 1, 3, 9, 29, 87, 261 | |||

Greek numeral | ΣΞΑ´ | |||

Roman numeral | CCLXI | |||

Binary |
100000101_{2} | |||

Ternary |
100200_{3} | |||

Quaternary |
10011_{4} | |||

Quinary |
2021_{5} | |||

Senary |
1113_{6} | |||

Octal |
405_{8} | |||

Duodecimal |
199_{12} | |||

Hexadecimal |
105_{16} | |||

Vigesimal |
D1_{20} | |||

Base 36 |
79_{36} |

**261** (**two hundred [and] sixty-one**) is a natural number proceeded by the number 260 and followed by 262. It has the prime factorization 3^{2}·29.

## Mathematical properties[edit]

There are six divisors of this number, the divisors being 1, 3, 9, 29, 87, and 261 itself.^{[1]} 261 is a deficient number, since 1 + 3 + 9 + 29 + 87 = 129 < 261.

261 is a lucky number, as well as an odious number, meaning it has an odd number of 1's in its binary expansion, which is 100000101_{2} (with 3 ones in it).^{[2]}

## In other fields[edit]

**261 may refer to...**

The years 261 AD or 261 BC.

The steam locomotive Milwaukee Road 261.

Alaska Airlines Flight 261, which crashed in the Pacific Ocean near Anacapa Island on January 31, 2000.

## References[edit]

**^**"Facts about the number 261".*Numbermatics - the number explorer*. Retrieved 2017-03-20.**^**"Number Gossip: 261".*www.numbergossip.com*. Retrieved 2017-03-20.