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 Brömssen, Jul 15 2023
STATUS
approved