Also the title of a much-loved song from Sesame Street, which goes a little something like this:
One two three four five, six seven eight nine ten, eleven twelve
One two three four five, six seven eight nine ten, eleven twe-e-e-e-e-e-lve
One two three four five, six seven eight nine ten, eleven TWELVE!
Accompanied, of course, by some really psychedelic pinball animation.