2009602

Appears in sequences

• Number of 2-element intersecting families (with not necessarily distinct sets) of an n-element set.at n=11A053154
• a(n) = (4^n + (-3)^n + 2^n + (-1)^n)/2.at n=10A317793
• Weighted count of equivalence classes of words w of length n+1 over {a, b, c, d, A, *} having exactly n letters, exactly one *, an even number of lowercase a's, and weight (-1)^(A(w)), where A(w) is the number of uppercase letters A.at n=10A390529