# 261 (number)

 ← 260 261 262 →
Cardinaltwo hundred sixty-one
Ordinal261st
(two hundred sixty-first)
Factorization32× 29
Divisors1, 3, 9, 29, 87, 261
Greek numeralΣΞΑ´
Roman numeralCCLXI
Binary1000001012
Ternary1002003
Quaternary100114
Quinary20215
Senary11136
Octal4058
Duodecimal19912
VigesimalD120
Base 367936

261 (two hundred [and] sixty-one) is a natural number proceeded by the number 260 and followed by 262. It has the prime factorization 32·29.

## Mathematical properties

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 nonagonal number, Harshad number, unique period in base 2, and the number of possible unfolded tesseract patterns.

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 1000001012 (with 3 ones in it).[2]

261 was once the lowest number not to have its own Wikipedia page, this making it a candidate for the lowest uninteresting Number according to the definition given by Alex Bellos.[3] As of September 2018, the smallest natural number without its own Wikipedia page is 262, and the smallest prime number without its own Wikipedia page is 283.

## In other fields

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. Madagascar’s country code

## References

1. ^ "Facts about the number 261". Numbermatics - the number explorer. Retrieved 2017-03-20.
2. ^ "Number Gossip: 261". www.numbergossip.com. Retrieved 2017-03-20.
3. ^ Bellos, Alex (June 2014). The Grapes of Math: How Life Reflects Numbers and Numbers Reflect Life. illus. The Surreal McCoy (1st Simon & Schuster hardcover ed.). N.Y.: Simon & Schuster. pp. 238 & 319 (quoting p. 319). ISBN 978-1-4516-4009-0.