A274376 - OEIS

%I #9 Jun 19 2016 17:28:23

%S 1,1,1,1,2,3,5,8,12,20,32,52,84,135,219,353,572,924,1495,2419,3912,

%T 6331,10240,16570,26807,43374,70178,113546,183721,297258,480974,

%U 778220,1259184,2037389,3296554,5333923,8630446,13964340,22594740,36559034,59153708,95712668

%N Number of modified skew Dyck paths such that the area between the x-axis and the path is n.

%C A modified skew Dyck path is a path in the first quadrant which begins at the origin, ends on the x-axis, consists of steps U=(1,1) (up), D=(1,-1) (down) and A=(-1,1) (anti-down) so that A and D steps do not overlap.

%F a(n) = Sum_{k=0..n} A274372(k,n).

%e                /\    /\

%e a(5) = 3:   /\/  \  /  \/\  /\/\/\/\/\  .

%e .

%e             /\

%e             \ \    /\          /\          /\

%e a(6) = 5:   /  \  /  \/\/\  /\/  \/\  /\/\/  \  /\/\/\/\/\/\  .

%Y Column sums of A274372.

%Y Cf. A230823.

%K nonn

%O 0,5

%A _Alois P. Heinz_, Jun 19 2016