A274988 - OEIS

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

(list; graph; refs; listen; history; text; internal format)

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

__ __ __

________ ____ __ ____ __ ____ __| ____ __| ____ __|

| __| | __| | | __| | | __| | | __| | | __| |

|____|__ |____|__| |____|__| |____|__| |____|__| |____|__|

| __| __ __|