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 A274821 Hexagonal spiral constructed on the nodes of the infinite triangular net in which each term is the least positive integer such that no diagonal contains a repeated term. 10
 1, 2, 3, 2, 3, 2, 3, 1, 4, 1, 5, 4, 6, 4, 5, 6, 4, 5, 7, 6, 7, 8, 5, 7, 6, 8, 7, 4, 1, 7, 6, 8, 1, 7, 8, 6, 5, 9, 2, 4, 7, 9, 2, 10, 8, 9, 3, 5, 10, 9, 3, 11, 12, 9, 10, 11, 13, 4, 9, 10, 8, 11, 10, 3, 5, 9, 6, 11, 3, 12, 10, 12, 1, 11, 8, 9, 7, 1, 10, 8, 11, 13, 8, 2, 5, 9, 6, 12, 2, 11, 13, 10, 6, 12, 11, 14, 13, 12, 14, 15 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Also spiral constructed on the infinite hexagonal grid in which each term is the least positive integer such that no diagonal of successive adyacent cells contains a repeated term. Every number is located in the center of a hexagonal cell. Every cell is also the center of three diagonals of successive adyacent cells. LINKS FORMULA a(n) = A274820(n) + 1. EXAMPLE Illustration of initial terms as a spiral: . .                  10 - 5 - 3 - 9 - 8 .                  /                 \ .                 9   4 - 7 - 8 - 6   10 .                /   /             \   \ .               3   1   6 - 4 - 5   7   2 .              /   /   /         \   \   \ .            11   7   4   2 - 3   1   5   9 .            /   /   /   /     \   \   \   \ .          12   6   5   3   1 - 2   4   8   7 .            \   \   \   \         /   /   / .             9   8   6   2 - 3 - 1   7   4 .              \   \   \             /   / .              10   1   4 - 5 - 7 - 6   2 .                \   \                 / .                11   7 - 8 - 6 - 5 - 9 .                  \ .                  13 - 4 - 9 - 10 - 8 . CROSSREFS Cf. A269526 (square array), A274640 (square spiral), A274651 (right triangle), A274820, A274920, A274921, A275606, A275610. Sequence in context: A145384 A117666 A274921 * A275720 A307200 A165587 Adjacent sequences:  A274818 A274819 A274820 * A274822 A274823 A274824 KEYWORD nonn AUTHOR Omar E. Pol, Jul 09 2016 STATUS approved

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Last modified January 18 19:40 EST 2020. Contains 331029 sequences. (Running on oeis4.)