Symbolic catalan number

[pelegm]

catalan_number should be able to accept a symbolic argument, just like harmonic_number and binomial (for example).

This effectively means making catalan_number a symbolic function.

Component: symbolics

Keywords: catalan

Issue created by migration from https://trac.sagemath.org/ticket/22028

[rwst]

Description changed:

--- 
+++ 
@@ -1 +1,3 @@
 `catalan_number` should be able to accept a symbolic argument, just like `harmonic_number` and `binomial` (for example).
+
+This effectively means making `catalan_number` a symbolic function.