# 261 (number)

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 ← 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
Octal4058
Duodecimal19912
Hexadecimal10516

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. 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).

## In other fields

261 may refer to:

Military / transportation
Space
• 261 Prymno, a minor planet
• Kosmos 261, a Soviet satellite launched in 1968
• NGC 261, a diffuse nebula located in the constellation Tucana
See also