The sequence

[lipreader]

The seqence 1,2,3,4,5,6,7,8,9,10 incorporates another sequence: 1,1,1,2,2,1,1,1,1,2. Why?

[Munden]

It is the number of times you have to put pen/pencil to paper to write the numbers.
It takes only one stroke of the pen to write 1,2,3,6,7,8,9, and two strokes to write the others usually, although I can write 5 with one stroke.