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Number T(n,k) of 2n-length strings of balanced parentheses of exactly k different types that are introduced in ascending order; triangle T(n,k), n>=0, 0<=k<=n, read by rows.
15

%I #28 Sep 28 2023 05:28:34

%S 1,0,1,0,2,2,0,5,15,5,0,14,98,84,14,0,42,630,1050,420,42,0,132,4092,

%T 11880,8580,1980,132,0,429,27027,129129,150150,60060,9009,429,0,1430,

%U 181610,1381380,2432430,1501500,380380,40040,1430,0,4862,1239810,14707550,37777740,33795762,12864852,2246244,175032,4862

%N Number T(n,k) of 2n-length strings of balanced parentheses of exactly k different types that are introduced in ascending order; triangle T(n,k), n>=0, 0<=k<=n, read by rows.

%C In general, column k>0 is asymptotic to (4*k)^n / (k!*sqrt(Pi)*n^(3/2)). - _Vaclav Kotesovec_, Jun 01 2015

%H Alois P. Heinz, <a href="/A253180/b253180.txt">Rows n = 0..140, flattened</a>

%F T(n,k) = A256061(n,k)/k! = Sum_{i=0..k} (-1)^i * C(k,i) * (k-i)^n * A000108(n) / A000142(n).

%e T(3,1) = 5: ()()(), ()(()), (())(), (()()), ((())).

%e T(3,2) = 15: ()()[], ()[](), ()[][], ()([]), ()[()], ()[[]], (())[], ([])(), ([])[], (()[]), ([]()), ([][]), (([])), ([()]), ([[]]).

%e T(3,3) = 5: ()[]{}, ()[{}], ([]){}, ([]{}), ([{}]).

%e Triangle T(n,k) begins:

%e 1;

%e 0, 1;

%e 0, 2, 2;

%e 0, 5, 15, 5;

%e 0, 14, 98, 84, 14;

%e 0, 42, 630, 1050, 420, 42;

%e 0, 132, 4092, 11880, 8580, 1980, 132;

%e 0, 429, 27027, 129129, 150150, 60060, 9009, 429;

%e ...

%p ctln:= proc(n) option remember; binomial(2*n, n)/(n+1) end:

%p A:= proc(n, k) option remember; k^n*ctln(n) end:

%p T:= (n, k)-> add(A(n, k-i)*(-1)^i/((k-i)!*i!), i=0..k):

%p seq(seq(T(n, k), k=0..n), n=0..10);

%t A[n_, k_] := A[n, k] = k^n*CatalanNumber[n]; T[0, 0] = 1; T[n_, k_] := Sum[A[n, k-i]*(-1)^i/((k-i)!*i!), {i, 0, k}]; Table[T[n, k], {n, 0, 10}, {k, 0, n}] // Flatten (* _Jean-François Alcover_, Jan 11 2017, adapted from Maple *)

%Y Columns k=0-10 give: A000007, A000108 (for n>0), A258390, A258391, A258392, A258393, A258394, A258395, A258396, A258397, A258398.

%Y Main diagonal gives A000108.

%Y First lower diagonal gives A002740(n+2).

%Y T(2n,n) gives A258399.

%Y Row sums give A064299.

%Y Cf. A000142, A256061.

%K nonn,tabl

%O 0,5

%A _Alois P. Heinz_, Mar 23 2015