Gessel sequence: the number of paths of length 2m in the plane, starting and ending at (0,1), with unit steps in the four directions (north, east, south, west) and staying in the region y > 0, x > -y.
A135404
Gessel sequence: the number of paths of length 2m in the plane, starting and ending at (0,1), with unit steps in the four directions (north, east, south, west) and staying in the region y > 0, x > -y.
Terms
- a(0) =1a(1) =2a(2) =11a(3) =85a(4) =782a(5) =8004a(6) =88044a(7) =1020162a(8) =12294260a(9) =152787976a(10) =1946310467a(11) =25302036071a(12) =334560525538
External references
- oeis: A135404