A274988 Square spiral reflection.

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.

Links

Table of n, a(n) for n=1..52.

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

Adjacent sequences: A274985 A274986 A274987 * A274989 A274990 A274991

Keyword

nonn

Author

Wesley Ivan Hurt, Dec 25 2016

Status

approved