- 11 is an odd prime number.
- 11 is the first number which cannot be counted with a human's ten fingers, using each finger as a tally mark. In English, it is the smallest positive integer requiring three syllables and the largest prime number with a single-morpheme name. Its etymology originates from a Germanic compound ainlif meaning "one left".
- 11 is the smallest non-trivial repdigit. Multiples of it up through 99 are also repdigits. 11 is a the first repunit number.
- 11 is also equal to \(n(2)\) in the block subsequence theorem.
- 11 is the largest known number n such that 2^n contains only even decimal digits. The decimal expansion of 2^11 is 2048, which contains all even digits. 2^n for all 11<n<1000000 contains at least one odd digit.
- In Greek-based number naming systems, 11 is associated with prefix "endeka-", and with prefix "undeci-" in Latin systems.
- Wiki user Denis Maksudov coined the name zeralum for this number, and it's equal to \(f_0(10)\) using the fast-growing hierarchy.
- In duodecimal, the digit eleven is normally represented by an upside-down 3 and is named "el".
In popular culture
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