130527

Appears in sequences

• Triangle read by rows: number of 0-1-2 trees (i.e., ordered trees with vertices of outdegrees 0, 1, or 2) with n edges and exactly k vertices that have 2 children, both being leaves (n >= 0, 0 <= k <= floor((n+2)/4)).at n=44A126191
• Number of 123 avoiding set partitions of [n].at n=11A270049
• a(0) = 1; a(n) = (1/3) * Sum_{k=1..n} binomial(n,k) * (4^k-1) * a(n-k).at n=6A337556