81747

Appears in sequences

• a(n+2) = 3*a(n) - a(n-2) with a(0) = 1, a(1) = 3, a(2) = 6.at n=18A018186
• Number of hierarchical orderings with at least 2 elements on each level for n unlabeled elements. Unlabeled analog of A097236.at n=22A109509
• a(1)=3, a(2)=1, a(n) = 3*a(n-1) + a(n-2).at n=10A189735