Number of rooted trees with 3 nodes of disjoint sets of labels with union {1..n}. If a node has an empty set of labels then it must have at least two children.
A005173
Number of rooted trees with 3 nodes of disjoint sets of labels with union {1..n}. If a node has an empty set of labels then it must have at least two children.
Terms
- a(0) =0a(1) =1a(2) =12a(3) =61a(4) =240a(5) =841a(6) =2772a(7) =8821a(8) =27480a(9) =84481a(10) =257532a(11) =780781a(12) =2358720a(13) =7108921a(14) =21392292a(15) =64307941a(16) =193185960a(17) =580082161a(18) =1741295052a(19) =5225982301a(20) =15682141200a(21) =47054812201a(22) =141181213812a(23) =423577195861
External references
- oeis: A005173