A303697 Number T(n,k) of permutations p of [n] whose difference between sum of up-jumps and sum of down-jumps equals k; triangle T(n,k), n>=0, min(0,1-n)<=k<=max(0,n-1), read by rows.

1, 1, 1, 0, 1, 1, 1, 2, 1, 1, 1, 4, 5, 4, 5, 4, 1, 1, 11, 19, 19, 20, 19, 19, 11, 1, 1, 26, 82, 100, 101, 100, 101, 100, 82, 26, 1, 1, 57, 334, 580, 619, 619, 620, 619, 619, 580, 334, 57, 1, 1, 120, 1255, 3394, 4339, 4420, 4421, 4420, 4421, 4420, 4339, 3394, 1255, 120, 1

Offset

0,8

Comments

An up-jump j occurs at position i in p if p_{i} > p_{i-1} and j is the index of p_i in the increasingly sorted list of those elements in {p_{i}, ..., p_{n}} that are larger than p_{i-1}. A down-jump j occurs at position i in p if p_{i} < p_{i-1} and j is the index of p_i in the decreasingly sorted list of those elements in {p_{i}, ..., p_{n}} that are smaller than p_{i-1}. First index in the lists is 1 here.

Links

Alois P. Heinz, Rows n = 0..125, flattened

Formula

T(n,0) = A153229(n) for n > 0.

T(n,1) = A005165(n-1) for n > 0.

T(n+1,n-1) = A000295(n).

T(n,k) = T(n,-k).

Sum_{k=0..n-1} k^2 * T(n,k) = A001720(n+2) for n>1.

Example

Triangle T(n,k) begins:
:                               1                             ;
:                               1                             ;
:                          1,   0,   1                        ;
:                     1,   1,   2,   1,   1                   ;
:                1,   4,   5,   4,   5,   4,   1              ;
:           1,  11,  19,  19,  20,  19,  19,  11,   1         ;
:      1,  26,  82, 100, 101, 100, 101, 100,  82,  26,  1     ;
:  1, 57, 334, 580, 619, 619, 620, 619, 619, 580, 334, 57, 1  ;

Maple

b:= proc(u, o) option remember; expand(`if`(u+o=0, 1,
      add(b(u-j, o+j-1)*x^(-j), j=1..u)+
      add(b(u+j-1, o-j)*x^( j), j=1..o)))
    end:
T:= n-> (p-> seq(coeff(p, x, i), i=ldegree(p)..degree(p)))(
        `if`(n=0, 1, add(b(j-1, n-j), j=1..n))):
seq(T(n), n=0..12);

Mathematica

b[u_, o_] := b[u, o] = Expand[If[u+o == 0, 1,
     Sum[b[u-j, o+j-1] x^-j, {j, 1, u}] +
     Sum[b[u+j-1, o-j] x^j, {j, 1, o}]]];
T[0] = {1};
T[n_] := x^n Sum[b[j-1, n-j], {j, 1, n}] // CoefficientList[#, x]& // Rest;
T /@ Range[0, 12] // Flatten (* Jean-François Alcover, Feb 20 2021, after Alois P. Heinz *) *)

Crossrefs

Row sums give A000142.

Cf. A000295, A001720, A005165, A008292, A081285, A153229, A291680, A291684, A291722, A316292, A316293, A321316.

Sequence in context: A355614 A140274 A095231 * A362827 A342413 A202019

Adjacent sequences: A303694 A303695 A303696 * A303698 A303699 A303700

Keyword

nonn,tabf

Author

Alois P. Heinz, Apr 28 2018

Status

approved