Number of 2n-step lattice paths from (0,0) to (0,0) using steps in {N, S, E, W} starting with East, then always moving straight ahead or turning left.
A228248
Number of 2n-step lattice paths from (0,0) to (0,0) using steps in {N, S, E, W} starting with East, then always moving straight ahead or turning left.
Terms
- a(0) =1a(1) =0a(2) =1a(3) =3a(4) =9a(5) =30a(6) =103a(7) =357a(8) =1257a(9) =4494a(10) =16246a(11) =59246a(12) =217719a(13) =805389a(14) =2996113a(15) =11200113a(16) =42047593a(17) =158452138a(18) =599113966a(19) =2272065638a(20) =8639763574a(21) =32933685102a(22) =125817012366a(23) =481631387438
External references
- oeis: A228248