Number of walks on square lattice. Column y=4 of A052174.

Terms

a(0) =1a(1) =5a(2) =35a(3) =140a(4) =720a(5) =2700a(6) =12375a(7) =45375a(8) =196625a(9) =715715a(10) =3006003a(11) =10930920a(12) =45048640a(13) =164105760a(14) =668144880a(15) =2441298600a(16) =9859090500a(17) =36149998500a(18) =145173803500a(19) =534239596880