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A132891 Sum of the heights of all left factors of Dyck paths of length n. 2

%I #19 Dec 19 2022 10:32:01

%S 1,3,6,14,28,61,121,257,508,1065,2103,4372,8634,17842,35254,72524,

%T 143396,293968,581630,1189102,2354168,4802331,9512984,19370764,

%U 38391332,78056544,154773135,314281350,623427154,1264546021,2509378855,5085153822,10094528146

%N Sum of the heights of all left factors of Dyck paths of length n.

%C See A132890 for the statistic "height" on left factors of Dyck paths.

%H Alois P. Heinz, <a href="/A132891/b132891.txt">Table of n, a(n) for n = 1..700</a>

%H Toufik Mansour and Gokhan Yilidirim, <a href="https://www.doi.org/10.3906/mat-1901-86">Longest increasing subsequences in involutions avoiding patterns of length three</a>, Turkish Journal of Mathematics (2019), Section 2.2.

%F a(n) = Sum_{k=1..n} k * A132890(n,k).

%e a(4)=14 because the six left factors of Dyck paths of length 4 are UDUD, UDUU, UUDD, UUDU, UUUD and UUUU, having heights 1, 2, 2, 2, 3 and 4, respectively.

%p v := ((1-sqrt(1-4*z^2))*1/2)/z: g := proc (k) options operator, arrow: v^k*(1+v)*(1+v^2)/((1+v^(k+1))*(1+v^(k+2))) end proc: T := proc (n, k) options operator, arrow; coeff(series(g(k), z = 0, 70), z, n) end proc: seq(add(k*T(n, k), k = 1 .. n), n = 1 .. 30);

%t b[x_, y_, k_] := b[x, y, k] = If[x == 0, z^k, If[y > 0, b[x - 2, y - 1, k], 0] + b[x - 2, y + 1, Max[y + 1, k]]];

%t T[n_] := Table[Coefficient[b[2n, 0, 0], z, i], {i, 1, n}];

%t a[n_] := T[n].Range[n];

%t Array[a, 33] (* _Jean-François Alcover_, Nov 10 2020, after _Alois P. Heinz_ in A132890 *)

%Y Cf. A132890.

%K nonn

%O 1,2

%A _Emeric Deutsch_, Sep 08 2007

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Last modified March 28 05:39 EDT 2024. Contains 371235 sequences. (Running on oeis4.)