%I #2 Mar 30 2012 16:51:15
%S 1,1,5,10,70,440,4280,44560,575920,8224640,134583680,2422639360,
%T 48232203520,1044455459840,24541639470080,620471213148160,
%U 16815502865029120,485975291876311040,14924807659888148480,485281269068774440960,16656262639515411742720,601766641496428795658240
%N 2^(n+1)*P_n(1/2) (see A155100).
%K nonn
%O -1,3
%A _N. J. A. Sloane_, Nov 05 2009