Number of walks on square lattice.

Terms

a(0) =10a(1) =70a(2) =308a(3) =1092a(4) =3414a(5) =9834a(6) =26752a(7) =69784a(8) =176306a(9) =434382a(10) =1048812a(11) =2490636a(12) =5833006a(13) =13500754a(14) =30933368a(15) =70255008a(16) =158335434a(17) =354419190a(18) =788529700a(19) =1744831060a(20) =3841983110a(21) =8422163130a(22) =18387829488