A368522 Triangular array T, read by rows: T(n,k) = number of sums |x-y| + |y-z| - |x-z| = 2n-2-k, where x,y,z are in {1,2,...,n}.

1, 2, 6, 2, 8, 17, 2, 8, 18, 36, 2, 8, 18, 32, 65, 2, 8, 18, 32, 50, 106, 2, 8, 18, 32, 50, 72, 161, 2, 8, 18, 32, 50, 72, 98, 232, 2, 8, 18, 32, 50, 72, 98, 128, 321, 2, 8, 18, 32, 50, 72, 98, 128, 162, 430, 2, 8, 18, 32, 50, 72, 98, 128, 162, 200, 561, 2

Offset

1,2

Comments

The rows are the reversals of the rows in A368521.

Links

Table of n, a(n) for n=1..67.

Example

First eight rows:
   1
   2   6
   2   8   17
   2   8   18   36
   2   8   18   32   65
   2   8   18   32   50   106
   2   8   18   32   50    72   161
   2   8   18   32   50    72    98    232
For n=2, there are 8 triples (x,y,z):
  111:  |x-y| + |y-z| - |x-z| = 0
  112:  |x-y| + |y-z| - |x-z| = 0
  121:  |x-y| + |y-z| - |x-z| = 2
  122:  |x-y| + |y-z| - |x-z| = 0
  211:  |x-y| + |y-z| - |x-z| = 0
  212:  |x-y| + |y-z| - |x-z| = 2
  221:  |x-y| + |y-z| - |x-z| = 0
  222:  |x-y| + |y-z| - |x-z| = 0
so row 2 of the array is (2,6), representing two 2s and six 0s.

Mathematica

t[n_] := t[n] = Tuples[Range[n], 3]
a[n_, k_] := Select[t[n], Abs[#[[1]] - #[[2]]] + Abs[#[[2]] - #[[3]]]
 - Abs[#[[1]] - #[[3]]] ==  2n-2-k &]
u = Table[Length[a[n, k]], {n, 1, 15}, {k, 0, 2 n - 2, 2}]
v = Flatten[u] (* sequence *)
Column[Table[Length[a[n, k]], {n, 1, 15}, {k, 0, 2 n - 2, 2}]]  (* array *)

Crossrefs

Cf. A084990 (column 1), A000578 (row sums), A001105 (limiting row), A368521.

Sequence in context: A069936 A043294 A365260 * A033641 A153190 A010240

Adjacent sequences: A368519 A368520 A368521 * A368523 A368524 A368525

Keyword

nonn,tabl

Author

Clark Kimberling, Jan 25 2024

Status

approved