OFFSET

0,2

COMMENTS

These subsets form an independence system, also called an abstract simplicial complex.

LINKS

EXAMPLE

For n = 5 the a(5) = 12 independent sets of {A007931(1), A007931(2), ..., A007931(5)} = {1, 2, 11, 12, 21} are:

1) {};

2) {1};

3) {2};

4) {2, 1};

5) {11};

6) {11, 2};

7) {12};

8) {12, 11};

9) {21};

10) {21, 11};

11) {21, 12}; and

12) {21, 12, 11}.

In each of these twelve sets, no string is a substring of any other. In particular, {12, 11, 2} is not an independent set because 2 is a substring of 12.

CROSSREFS

KEYWORD

nonn,base

AUTHOR

Peter Kagey, May 19 2023

EXTENSIONS

More terms from Pontus von BrÃ¶mssen, Jul 15 2023

STATUS

approved