Problem #WSP-000268

Problems Discrete Mathematics Combinatorics

Problem

How many subsets are there of {1,2,...,10} (the integers from 1 to 10 inclusive) containing no consecutive digits? That is, we do count {1,3,6,8} but do not count {1,3,6,7}.
For example, when n=3, we have 8 subsets overall but only 5 contain no consecutive integers. The 8 subsets are (the empty set), {1}, {2}, {3}, {1,3}, {1,2}, {2,3} and {1,2,3}, but we exclude the final three of these.