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%I #3 Mar 30 2012 16:48:55

%S 1,4,12,40,120,396,1260,4176,13788,46240,155496,527160,1792804,

%T 6125028,20986020,72117632,248396792,857402748,2964896876,10269550040,

%U 35622420288,123727866768,430254861944,1497796242288,5219231003500

%N n*A000084(n).

%D Z. A. Lomnicki, Two-terminal series-parallel networks, Adv. Appl. Prob., 4 (1972), 109-150.

%Y Cf. A000084, A006349, A006350, A058351, A058352, A000669.

%K nonn

%O 1,2

%A _N. J. A. Sloane_, Dec 16 2000