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%I M1145 #24 Oct 20 2023 22:22:08
%S 1,1,2,4,8,17,38,89,208
%N Number of n-level ladder expressions with A002193.
%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. A003008.
%K nonn,more
%O 1,3
%A _N. J. A. Sloane_