261 (two hundred [and] sixty-one) is the natural number following 260 and preceding 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, 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).
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