Wedderburn–Etherington number

In mathematics and computer science, the Wedderburn–Etherington numbers are an integer sequence named after Ivor Malcolm Haddon Etherington and Joseph Wedderburn that can be used to count certain kinds of binary trees. 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, ... (OEIS: A001190)
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