A104570 Triangle read by rows: T(i,j) is the (i,j)-entry (1 <= j <= i) of the product R*Q of the infinite lower triangular matrices R = [1; 1,1; 1,1,1; 1,1,1,1; ...] and Q = [1; 1,3; 1,3,1; 1,3,1,3; ...].

1, 2, 3, 3, 6, 1, 4, 9, 2, 3, 5, 12, 3, 6, 1, 6, 15, 4, 9, 2, 3, 7, 18, 5, 12, 3, 6, 1, 8, 21, 6, 15, 4, 9, 2, 3, 9, 24, 7, 18, 5, 12, 3, 6, 1, 10, 27, 8, 21, 6, 15, 4, 9, 2, 3, 11, 30, 9, 24, 7, 18, 5, 12, 3, 6, 1, 12, 33, 10, 27, 8, 21, 6, 15, 4, 9, 2, 3, 13, 36, 11, 30, 9, 24, 7, 18, 5, 12, 3, 6, 1

Offset

1,2

Links

Table of n, a(n) for n=1..91.

Formula

Even columns (offset) = 1, 2, 3, ...; while odd columns = 3, 6, 9, ...

T(i,j) = i-j+1 if j <= i and j is odd; 3(i-j+1) if j <= i and j is even. - Emeric Deutsch, Mar 23 2005

Example

First few rows of the triangle:
  1;
  2, 3;
  3, 6, 1;
  4, 9, 2, 3;
  ...

Maple

T:=proc(i, j) if j>i then 0 elif j mod 2 = 1 then i-j+1 else 3*(i-j+1) fi end:for i from 1 to 14 do seq(T(i, j), j=1..i) od; # yields sequence in triangular form # Emeric Deutsch, Mar 23 2005

Mathematica

Q[i_, j_] := If[j <= i, 2 + (-1)^j, 0];
R[i_, j_] := If[j <= i, 1, 0];
T[i_, j_] := Sum[R[i, k]*Q[k, j], {k, 1, 13}];
Table[T[i, j], {i, 1, 13}, {j, 1, i}] // Flatten (* Jean-François Alcover, Jul 24 2024~ *)

Crossrefs

Cf. A035608, A074377, A104569.

Row sums yield A035608. The product Q*R yields A104569.

Sequence in context: A046826 A323713 A054892 * A103356 A345385 A071915

Adjacent sequences: A104567 A104568 A104569 * A104571 A104572 A104573

Keyword

nonn,tabl

Author

Gary W. Adamson, Mar 16 2005

Extensions

More terms from Emeric Deutsch, Mar 23 2005

Status

approved