29 Apr
2003
29 Apr
'03
4:43 a.m.
Isn't that the subject of the following well-known article? %D A003018 R. K. Guy and J. L. Selfridge, The nesting and roosting habits of the laddered parenthesis. Amer. Math. Monthly 80 (1973), 868-876. (there are numerous references to it in the OEIS) NJAS