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 A308626 Van Eck sequence on a square spiral on a 2-D grid. 2
 0, 0, 1, 0, 1, 2, 0, 2, 2, 1, 3, 0, 2, 4, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,6 COMMENTS Fill a 2-dimensional board made from square cells with numbers using the following rules: - start from 0; - if the number just written is new then the next number is 0; - if the number just written was present on the board before, the next number is the distance from its closest occurrence, counting cells you need to pass through to reach it .   1     0---->2---->2---->1   ^     ^                 |   |     |                 |   |     |                 v   1     2     0---->0     3   ^     ^   Start   |     |   |     |           |     |   |     |           v     v   1     1<----0<----1     0   ^                       |   |                       |   |                       v   1<----1<----0<----4<----2 . a(n) = 1 for all n >= 17 because the previous 1 will always be adjacent to another 1. The version of this sequence using the Moore neighborhood (vertex adjacency) consists of 0, 0, 1, 0, 1, 2, 0, 1, 2, 2, and then an infinite number of 1's. - Charlie Neder, Jun 11 2019 LINKS CROSSREFS Cf. A181391, A308625. Sequence in context: A029314 A071635 A156643 * A268755 A128664 A003823 Adjacent sequences:  A308623 A308624 A308625 * A308627 A308628 A308629 KEYWORD nonn AUTHOR Jacek Sandomierz, Jun 11 2019 STATUS approved

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Last modified November 29 08:38 EST 2020. Contains 338762 sequences. (Running on oeis4.)