A339565 - OEIS

%I #25 May 30 2022 08:05:10

%S 1,3,17,101,627,3999,25955,170571,1131433,7559301,50795985,342935689,

%T 2324278669,15804931797,107775401349,736723618773,5046774983235,

%U 34636814325087,238114193665451,1639378334244867,11301978856210543,78010917772099207,539055832175992119

%N Number of lattice paths from (0,0) to (n,n) using steps (0,1), (1,0), (1,1), (1,2), (2,1).

%H Alois P. Heinz, <a href="/A339565/b339565.txt">Table of n, a(n) for n = 0..1179</a> (first 101 terms from Kent Mei)

%F a(n) = [(x*y)^n] 1/(1-x-y-x*y-x*y^2-x^2*y). - _Alois P. Heinz_, Dec 09 2020

%p a:= proc(n) local t; 1/(1-x-y-x*y-(x*y^2)-(x^2*y));

%p       for t in [x, y] do coeftayl(%, t=0, n) od

%p     end:

%p seq(a(n), n=0..25);  # _Alois P. Heinz_, Dec 09 2020

%p # second Maple program:

%p b:= proc(l) option remember; `if`(l[2]=0, 1,

%p       add((f-> `if`(f[1]<0, 0, b(f)))(sort(l-h)), h=

%p       [[1, 0], [0, 1], [1$2], [1, 2], [2, 1]]))

%p     end:

%p a:= n-> b([n$2]):

%p seq(a(n), n=0..25);  # _Alois P. Heinz_, Dec 09 2020

%p # third Maple program:

%p a:= proc(n) option remember; `if`(n<3, [1, 3, 17][n+1],

%p       ((6*n-3)*a(n-1)+(7*n-7)*a(n-2)+(4*n-6)*a(n-3))/n)

%p     end:

%p seq(a(n), n=0..25);  # _Alois P. Heinz_, Dec 09 2020

%t b[l_] := b[l] = If[l[[2]] == 0, 1,

%t      Sum[Function[f, If[f[[1]] < 0, 0, b[f]]][Sort[l - h]], {h,

%t      {{1, 0}, {0, 1}, {1, 1}, {1, 2}, {2, 1}}}]];

%t a[n_] := b[{n, n}];

%t Table[a[n], {n, 0, 25}] (* _Jean-François Alcover_, May 30 2022, after _Alois P. Heinz_ *)

%Y Cf. A000984, A001850, A137635, A339390.

%K nonn

%O 0,2

%A _Kent Mei_, Dec 08 2020