A131406 3*A128174 - 2*A000012(signed).

1, 2, 1, 1, 2, 1, 2, 1, 2, 1, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1

Offset

1,2

Comments

Row sums = A032766, congruent to {0,1} mod 3: (1, 3, 4, 6, 7, 9, 10,...).

Sequence array for the expansion of (1+2x)/(1-x^2). A105476 is an eigensequence. [From Paul Barry, Nov 03 2010]

Links

Table of n, a(n) for n=1..55.

Formula

3*A128174 - 2*A000012(signed + - + 1 by columns). (1, 2, 1, 2, 1,...) in every column.

Triangle T(n,k)=if(k<=n,(3-(-1)^(n-k))/2). [From Paul Barry, Nov 03 2010]

Example

First few rows of the triangle are:
1;
2, 1;
1, 2, 1;
2, 1, 2, 1;
1, 2, 1, 2, 1;
2, 1, 2, 1, 2, 1;
...

Mathematica

T[n_, k_] := Mod[n-k, 2]+1; Table[T[n, k], {n, 1, 10}, {k, 1, n}] // Flatten (* Jean-François Alcover, Nov 17 2016 *)

Crossrefs

Cf. A128174, A000012, A032766.

Sequence in context: A001030 A246140 A071709 * A029440 A061337 A352767

Adjacent sequences: A131403 A131404 A131405 * A131407 A131408 A131409

Keyword

nonn,tabl

Author

Gary W. Adamson, Jul 07 2007

Status

approved