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A344548
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Lexicographically earliest sequence of nonnegative terms forming a clockwise square spiral when nothing else is read except the parity of the digits (see the Comments section).
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4
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0, 1, 3, 2, 5, 4, 7, 6, 8, 9, 20, 10, 22, 12, 24, 14, 26, 21, 28, 40, 16, 42, 44, 18, 46, 48, 30, 60, 62, 23, 64, 66, 68, 32, 80, 82, 84, 34, 86, 88, 201, 200, 202, 203, 204, 206, 205, 208, 220, 222, 36, 224, 226, 207, 228, 240, 242, 25, 244, 246, 248, 27, 260, 262, 264, 209, 266, 268, 280, 221, 282, 284
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,3
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COMMENTS
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An even digit turns the pencil 0 degrees to the right, then advances 1 unit; an odd digit turns the pencil 90 degrees to the right, then advances 1 unit.
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LINKS
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EXAMPLE
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The pencil points towards the East before the start. The 0 doesn't change its orientation and a 1-unit line directed towards the East is traced. As 1 is odd, the pencil turns 90 degrees towards the South and a 1-unit line is traced. As 3 is odd, the pencil turns 90 degrees towards the West and a 1-unit line is traced. As 2 is even, the pencil doesn't change its orientation (towards the West) and a 1-unit line is traced. As 5 is odd, the pencil turns 90 degrees towards the North and a 1-unit line is traced. As 4 is even, the pencil doesn't change its orientation (towards the North) and a 1-unit line is traced. Etc.
When it comes to a(11) = 20, the pencil reads 2 (even), doesn't change its orientation and advances 1 square, then reads 0 (even), doesn't change its orientation and advances 1 square again.
When it comes to a(12) = 10, the pencil reads 1 (odd), turns to the right and advances 1 square, then reads 0 (even), doesn't change its orientation and advances 1 square. Etc.
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CROSSREFS
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Cf. A344547 (same idea with terms), A174344 (an example of a clockwise square spiral).
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KEYWORD
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base,nonn
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AUTHOR
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STATUS
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approved
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