For example, the string "49142" has the following 3-digit series:
- 491
- 914
- 142
And the following 4-digit series:
- 4914
- 9142
And if you ask for a 6-digit series from a 5-digit string, you deserve whatever you get.
Note that these series are only required to occupy adjacent positions in the input; the digits need not be numerically consecutive.