Combinators and Catalan numbers

I seem to run into Catalan numbers fairly regularly. This evening I ran into Catalan numbers while reading Stephen Wolfram’s book Combinators: A Centennial View [1]. Here’s the passage. The number of combinator expressions of size n grows like {2, 4, 16, 80, 448, 2688, 16896, 109824, 732160, 4978688} or in general 2n CatalanNumber[n-1] = […] The post Combinators and Catalan numbers first appeared on John D. Cook....

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