261 (number)

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]

In other fields[]

261 may refer to:

• 261 AD, a calendar year
• 261 AM, a radio frequency
• 261 BC, a calendar year
• 261 Fearless, a non-profit organization started by Kathrine Switzer, who in 1967 wore bib number 261 when she became the first woman to run the Boston Marathon as a numbered entrant
• +261, a country calling code; see telephone numbers in Madagascar
• H.261, an video compression standard

Military / transportation

• Flight 261, several airliner incidents
• German submarine U-261, which was sunk in 1942
• KiHa 261 series, a type of diesel train in Japan
• Messerschmitt Me 261, an airplane of the late 1930s
• Milwaukee Road 261, a restored steam locomotive built in 1944
• No. 261 Squadron RAF, of World War I and World War II
• VMM-261, a United States Marine Corps squadron

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

• List of highways numbered 261
• All pages with titles containing 261

References[]