%I #4 Mar 30 2012 16:47:42

%S 1,2,2,6,2,18,2,46,14,126,2,454,2,1266,134,4222,2,14202,2,46406,1274,

%T 155502,2,531790,122,1792810,13802,6126334,2,21032794,2,72121854,

%U 155510,248396798,1382,857944150,2,2964896882,1792818,10269600622

%N Numbers d_n used in recurrence for series-parallel numbers.

%D J. Riordan, An Introduction to Combinatorial Analysis, foot of p. 141.

%F G.f.: S'*(1-S)/(1+S), where S = g.f. for A000084.

%K nonn,easy

%O 0,2

%A _N. J. A. Sloane_.