  A recursively palindromic (RP) word is one that is a palindrome and whose
left half-word and right half-word are each RP. Thus ABACABA is, and MADAM is
not, an RP word. We count RP words of given length over a finite alphabet and
RP compositions of an integer. We use the same method to determine the parity
of the Catalan numbers.

Combinatorics