Instead of describing the position of a particular letter in a French sentence—or in any other language—we can describe the positions occupied by particular digits in a number sequence. This is precisely what happens with the "1s" in the following sequence S1: they occupy the positions given by the sequence itself!
S1 = 1, 3, 10, 6, 11, 7, 21, 13, 15, 17, 19, 101, 24, 100, 29, 102, 34, 103, 39, 104, 44, 105, 49… Sure enough, there is a "1" in position 1, another in position 3, then in position 10, position 6, position 11…
The same holds for the positions of the "2s" in sequence S2: S2 = 2, 20, 1, 6, 21, 9, 22, 10, 15, 23, 19, 222, 220, 25, 27, 29, 32, 35, 200, 40, 201, 45, 202, 47… The sequences for the other eight digits (including "0") can be found on the Online Encyclopedia of Integer Sequences website (OEIS; see, for example, ).
Names for numbers
One interesting class of numbers is that of autobiographical integers. The smallest is 22. It should be read as "two 2s," which is true: 22 does indeed contain two instances of the digit 2.
