%I #8 Feb 23 2014 05:05:54
%S 0,0,0,1,2,6,17,57,191,663,2415,9108,35695,143989,599802,2566917,
%T 11298164,50967216,235745644,1115324000,5397332497,26669487517,
%U 134528555379,691856601631,3626390958551,19353306241764,105122093620388,580689432523534,3260906342453966
%N Number of standard Young tableaux with n cells and exactly two successions.
%C A succession is a pair of cells (v, v+1) lying in the same row.
%C Also number of ballot sequences having two flat steps.
%C Third column (k=2) of A238125.
%Y Cf. A237770 (no successions), A238126 (one succession).
%K nonn
%O 0,5
%A _Joerg Arndt_ and _Alois P. Heinz_, Feb 21 2014