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 A341440 Square spiral of positive integers built by greedy algorithm such that each positive integer appears exactly three times and within a 2 X 2 square area. 1
 1, 1, 1, 2, 2, 2, 3, 3, 4, 4, 4, 5, 5, 5, 6, 6, 7, 7, 8, 8, 9, 3, 10, 10, 11, 11, 11, 12, 12, 13, 13, 13, 14, 6, 15, 15, 16, 7, 17, 8, 9, 9, 18, 18, 19, 10, 20, 20, 21, 21, 21, 22, 12, 23, 23, 24, 24, 24, 14, 14, 25, 15, 16, 16, 26, 26, 17, 17, 27, 27, 28, 28 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 COMMENTS The motivation for this sequence is to tile a square spiral with L triominos; for any n > 0, the location of the three occurrences of n correspond to the n-th tile. Graphically, these tiles occupy four periodic regions (see Illustration in Links section). LINKS Rémy Sigrist, Table of n, a(n) for n = 0..10200 Rémy Sigrist, Colored representation of the tiling (black pixels indicate insertion points, the color is function of the insertion point and the tile orientation) Rémy Sigrist, PARI program for A341440 EXAMPLE The spiral begins:       16--15--15---6--14--13--13        |                       |        7   7---6---6---5---5  13        |   |               |   |       17   7   2---2---1   5  12        |   |   |       |   |   |        8   8   2   1---1   4  12        |   |   |           |   |        9   8   3---3---4---4  11        |   |                   |        9   9---3--10--10--11--11        |       18--18--19--10--20--20--21 PROG (PARI) See Links section. CROSSREFS See A341291 for another tiling with L triominos. Sequence in context: A032634 A057366 A189663 * A061375 A029920 A100719 Adjacent sequences:  A341437 A341438 A341439 * A341441 A341442 A341443 KEYWORD nonn AUTHOR Rémy Sigrist, Feb 12 2021 STATUS approved

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Last modified June 22 14:22 EDT 2021. Contains 345380 sequences. (Running on oeis4.)