|Cardinal||two hundred sixty|
(two hundred sixtieth)
|Factorization||22× 5 × 13|
260 is also the magic constant of the Franklin magic square devised by Benjamin Franklin.
The minor diagonal gives 260, and in addition a number of combinations of two half diagonals of four numbers from a corner to the center give 260.
261 = 32·29, lucky number, nonagonal number, Harshad number, unique period in base 2, number of possible unfolded tesseract patterns. 261 is 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.
263 has its own article. 263 is a prime, safe prime, happy number, sum of five consecutive primes (43 + 47 + 53 + 59 + 61), balanced prime, Chen prime, Eisenstein prime with no imaginary part, strictly non-palindromic number, Bernoulli irregular prime, Euler irregular prime, Gaussian prime, full reptend prime, Solinas prime, Ramanujan prime.
264 equals the sum of the squares of the digits of its own square in base 15. This property is shared with 1, 159, 284, 306 and 387.
266 = 2·7·19, sphenic number, Harshad number, nontotient, noncototient, self number, repdigit in base 11 (222). 266 is also the index of the largest proper subgroups of the sporadic group known as the Janko group J1.
- 267 is also the area code for Pennsylvania, USA (Philadelphia area including its suburbs in eastern Montgomery County and most of Bucks County, overlays with 215)
269 has its own article. 269 is a prime, twin prime with 271, sum of three consecutive primes (83 + 89 + 97), Chen prime, Eisenstein prime with no imaginary part, highly cototient number, strictly non-palindromic number, full reptend prime
- 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.
- Wells, D. The Penguin Dictionary of Curious and Interesting Numbers London: Penguin Group. (1987): 138
- Number of groups of order n