Hello Math-Fun, The seq here: http://www.research.att.com/~njas/sequences/A046043 could be extended in a certain way, asking to self- describe substrings like "10", "11", etc. I found those: | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | --------------------------------------------- | 5 | 3 | 1 | 1 | 0 | 1 | 0 | 0 | 0 | 0 | 2 | | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | --------------------------------------------- | 6 | 2 | 2 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 1 | | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 |11 | ------------------------------------------------- | 5 | 4 | 1 | 0 | 1 | 1 | 0 | 0 | 0 | 0 | 2 | 1 | Are there more? Best, É. --- A longer explanation in french here: http://www.cetteadressecomportecinquantesignes.com/SubStrings.htm