Editing Wedderburn–Etherington number (section)

{{Short description|Number that can be used to count certain kinds of binary trees}}
In [[mathematics]] and [[computer science]], the '''Wedderburn–Etherington numbers''' are an [[integer sequence]] named after [[Ivor Malcolm Haddon Etherington]]<ref name="e37">{{citation
 | last = Etherington | first = I. M. H. | author-link = Ivor Malcolm Haddon Etherington
 | doi = 10.2307/3605743
 | issue = 242
 | journal = [[Mathematical Gazette]]
 | pages = 36–39, 153
 | title = Non-associate powers and a functional equation
 | volume = 21
 | year = 1937| jstor = 3605743 | s2cid = 126360684 }}.</ref><ref name="e39">{{citation
 | last = Etherington | first = I. M. H. | author-link = Ivor Malcolm Haddon Etherington
 | issue = 2
 | journal = Proc. R. Soc. Edinburgh
 | pages = 153–162
 | title = On non-associative combinations
 | volume = 59
 | year = 1939| doi = 10.1017/S0370164600012244 }}.</ref> and [[Joseph Wedderburn]]<ref name="w">{{citation
 | last = Wedderburn | first = J. H. M. | author-link = Joseph Wedderburn
 | doi = 10.2307/1967710
 | issue = 2
 | journal = [[Annals of Mathematics]]
 | pages = 121–140
 | title = The functional equation <math>g(x^2) = 2ax + [g(x)]^2</math>
 | volume = 24
 | year = 1923| jstor = 1967710 }}.</ref> that can be used to count certain kinds of [[binary tree]]s. The first few numbers in the sequence are
:0, 1, 1, 1, 2, 3, 6, 11, 23, 46, 98, 207, 451, 983, 2179, 4850, 10905, 24631, 56011, ... ({{OEIS2C|A001190}})