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 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.