%I M1147 #25 Jan 05 2025 10:15:01

%S 1,1,2,4,8,17,39,90,213

%N Number of n-level ladder expressions with A030798.

%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

%H R. K. Guy and J. L. Selfridge, <a href="http://www.jstor.org/stable/2319392">The nesting and roosting habits of the laddered parenthesis</a>, Amer. Math. Monthly 80 (8) (1973), 868-876.

%H R. K. Guy and J. L. Selfridge, <a href="/A003018/a003018.pdf">The nesting and roosting habits of the laddered parenthesis</a>. (annotated cached copy)

%H <a href="/index/Par#parens">Index entries for sequences related to parenthesizing</a>

%Y Cf. A082499.

%K nonn,more

%O 1,3

%A _N. J. A. Sloane_