A343853 Irregular triangle read by rows: the n-th row gives the row indices of the matrix of 1..n^2 filled successively back and forth along antidiagonals.

1, 1, 1, 2, 2, 1, 1, 2, 3, 2, 1, 2, 3, 3, 1, 1, 2, 3, 2, 1, 1, 2, 3, 4, 4, 3, 2, 3, 4, 4, 1, 1, 2, 3, 2, 1, 1, 2, 3, 4, 5, 4, 3, 2, 1, 2, 3, 4, 5, 5, 4, 3, 4, 5, 5, 1, 1, 2, 3, 2, 1, 1, 2, 3, 4, 5, 4, 3, 2, 1, 1, 2, 3, 4, 5, 6, 6, 5, 4, 3, 2, 3, 4, 5, 6, 6, 5, 4, 5, 6, 6

Offset: 1

Author

Stefano Spezia, May 01 2021

Keywords

• nonn
• look
• tabf

Examples

			The triangle begins:
1
1   1   2   2
1   1   2   3   2   1   2   3   3
1   1   2   3   2   1   1   2   3   4   4   3   2   3   4   4
...
		

Links

• Stefano Spezia, First 30 rows of the triangle, flattened

Crossrefs

Cf. A000290 (row length), A002411 (row sums), A060747 (number of antidiagonals), A078475, A319573, A343854 (column indices).

Programs

Mathematica

a={};For[n=1,n<=6,n++,For[d=1,d<=n,d++, If[OddQ[d],i=d;For [k=1,k<=d,k++, AppendTo[a,i-k+1]],i=1;For[k=1,k<=d,k++, AppendTo[a,i+k-1]]]];For[d=n+1,d<=2n-1,d++, If[OddQ[d],i= n; For[k=1,k<=2n-d,k++,AppendTo[a,i-k+1]],If[EvenQ[d],i=d-n+1;For[k=1,k<=2n-d,k++, AppendTo[a,i+k-1]]]]]]; a