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A274988
Square spiral reflection.
0
1, 3, 5, 7, 9, 9, 9, 9, 11, 13, 13, 15, 17, 19, 21, 23, 25, 27, 27, 27, 27, 27, 27, 27, 29, 31, 33, 33, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 53, 53, 53, 53, 53, 53, 53, 53, 53, 55, 57, 59, 61
OFFSET
1,2
COMMENTS
Draw a square spiral growing by a unit line segment on each step, and at the same time, draw another square spiral in the opposite direction (again using a unit line segment) that turns after the first step (see example). a(n) is the number of unit line segments remaining after the n-th step. Note that overlapping line segments are counted once.
EXAMPLE
__ ____ ____ ____ ____ ____
__ __| __| __| | __| | __| | __| | __|
| __| ____| |____| |____| |____| |____|
n=1 n=2 n=3 n=4 n=5 n=6 n=7 n=8
--
__ __ __
________ ____ __ ____ __ ____ __| ____ __| ____ __|
| __| | __| | | __| | | __| | | __| | | __| |
|____|__ |____|__| |____|__| |____|__| |____|__| |____|__|
| __| __ __|
n=9 n=10 n=11 n=12 n=13 n=14
CROSSREFS
Sequence in context: A139081 A196189 A206543 * A265509 A265527 A217250
KEYWORD
nonn
AUTHOR
Wesley Ivan Hurt, Dec 25 2016
STATUS
approved