Wedderburn-Etherington number

The nth Wedderburn-Etherington numberMathworldPlanetmath counts how many weakly binary trees can be constructed such that each graph vertex (not counting the root vertex) is adjacent to no more than three other such vertices, for a given number n of nodes. The first few Wedderburn-Etherington numbers are 1, 1, 1, 2, 3, 6, 11, 23, 46, 98, 207, 451, 983, etc. listed in A001190 of Sloane’s OEIS. Michael Somos gives the following recurrence relations:




with a1=a2=1 in both relationsMathworldPlanetmath.

Title Wedderburn-Etherington number
Canonical name WedderburnEtheringtonNumber
Date of creation 2013-03-22 16:49:32
Last modified on 2013-03-22 16:49:32
Owner PrimeFan (13766)
Last modified by PrimeFan (13766)
Numerical id 6
Author PrimeFan (13766)
Entry type Definition
Classification msc 05A15
Synonym Wedderburn Etherington number
Synonym Etherington-Wedderburn number