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A343558 Irregular triangle read by rows: the n-th row gives the row indices of the consecutive elements of the spiral of the n X n matrix defined in A126224. 2
1, 1, 1, 2, 2, 1, 1, 1, 2, 3, 3, 3, 2, 2, 1, 1, 1, 1, 2, 3, 4, 4, 4, 4, 3, 2, 2, 2, 3, 3, 1, 1, 1, 1, 1, 2, 3, 4, 5, 5, 5, 5, 5, 4, 3, 2, 2, 2, 2, 3, 4, 4, 4, 3, 3, 1, 1, 1, 1, 1, 1, 2, 3, 4, 5, 6, 6, 6, 6, 6, 6, 5, 4, 3, 2, 2, 2, 2, 2, 3, 4, 5, 5, 5, 5, 4, 3, 3, 3, 4, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

LINKS

Stefano Spezia, First 30 rows of the triangle, flattened

EXAMPLE

The triangle begins

1

1   1   2   2

1   1   1   2   3   3   3   2   2

1   1   1   1   2   3   4   4   4   4   3   2   2   2   3   3

...

MATHEMATICA

a:={}; nmax:=6; For[n=1, n<=nmax, n++, For[s=1, s<=2n-1, s++, If[OddQ[s] &&Mod[s, 4]==1, k=Ceiling[s/4]; For[i=1, i<=Ceiling[n-s/2], i++, AppendTo[a, k]], If[EvenQ[s]&&Mod[s, 4]==2, For[i=1, i<=Ceiling[n-s/2], i++, AppendTo[a, k+i]]; k+=Ceiling[n-s/2], If[EvenQ[s]&&Mod[s, 4]==0, For[i=1, i<=Ceiling[n-s/2], i++, AppendTo[a, k-i]]; k=k-i+1, For[i=1, i<=Ceiling[n-s/2], i++, AppendTo[a, k]]]]]]]; a

CROSSREFS

Cf. A000290 (row length), A002265, A002411 (row sums), A010873, A060747, A126224, A343559 (column indices).

Sequence in context: A047070 A071127 A029381 * A297877 A027926 A114730

Adjacent sequences:  A343555 A343556 A343557 * A343559 A343560 A343562

KEYWORD

nonn,tabf

AUTHOR

Stefano Spezia, Apr 19 2021

STATUS

approved

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Last modified September 28 19:16 EDT 2021. Contains 347717 sequences. (Running on oeis4.)