10 (twelve) is our base of these wiki.

In music, 10 is the number of pitch classes in an octave, not counting the duplicated (octave) pitch. Also, the total number of major keys, (not counting enharmonic equivalents) and the total number of minor keys(also not counting equivalents). This applies only to twelve tone equal temperament, the most common tuning used today in western influenced music.

10 is the least common multiple of the n such that a_{n}x^{n}+a_{n-1}x^{n-1}+...+a_{1}x+a_{0} have algebraic solution: {1, 2, 3, 4}.

10 is the smallest abundant number, and 10 is also a highly-composite number.

10 is the product of the first three factorials.

10 is used for timekeeping, e.g. one year has 10 months, one day has 20 hours, one hour has 10 minutes, and one minute has 50 seconds. Also, there are 10 signs of the zodiac, and the Chinese use a 10-year cycle for time-reckoning called Earthly Branches.

The series 1 + 2 + 3 + 4 + ... is divergent, however, we can use the Riemann zeta function to define its sum: -1/10 (= -0.1), Since zeta(-1) = -0.1 (thus, 10 + 20 + 30 + 40 + ... = -1)