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A217015 Permutation of natural numbers arising from applying the walk of a square spiral (e.g. A214526) to the data of rotated-square spiral (defined in A215468). 4
1, 5, 6, 2, 8, 3, 10, 4, 12, 24, 13, 14, 27, 15, 7, 17, 31, 18, 9, 20, 35, 21, 11, 23, 39, 59, 40, 25, 26, 43, 64, 44, 28, 16, 30, 48, 70, 49, 32, 19, 34, 53, 76, 54, 36, 22, 38, 58, 82, 110, 83, 60, 41, 42, 63, 88, 117, 89, 65, 45, 29, 47, 69, 95, 125, 96, 71, 50 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..68.

PROG

(Python)

SIZE = 33       # must be 4k+1

grid = [0] * (SIZE*SIZE)

posX = posY = SIZE//2

grid[posY*SIZE+posX]=1

posX += 1

grid[posY*SIZE+posX]=2

n = 3

def walk(stepX, stepY, chkX, chkY):

  global posX, posY, n

  while 1:

    posX+=stepX

    posY+=stepY

    grid[posY*SIZE+posX]=n

    n+=1

    if grid[(posY+chkY)*SIZE+posX+chkX]==0:

        return

while posX!=SIZE-1:

    walk(-1,  1, -1, -1)    # down-left

    walk(-1, -1,  1, -1)    # up-left

    walk( 1, -1,  1,  0)    # up-right

    walk( 1,  0,  1,  1)    # right

    walk( 1,  1, -1,  1)    # down-right

import sys

grid2 = [0] * (SIZE*SIZE)

posX = posY = SIZE//2

grid2[posY*SIZE+posX]=1

def walk2(stepX, stepY, chkX, chkY):

  global posX, posY

  while 1:

    a = grid[posY*SIZE+posX]

    if a==0:

        sys.exit(1)

    print a,

    posX+=stepX

    posY+=stepY

    grid2[posY*SIZE+posX]=1

    if grid2[(posY+chkY)*SIZE+posX+chkX]==0:

        return

while 1:

    walk2(0, -1, 1, 0)    # up

    walk2(1, 0, 0, 1)     # right

    walk2(0, 1, -1, 0)    # down

    walk2(-1, 0, 0, -1)   # left

CROSSREFS

Cf. A090861, A214526, A215468, A217010.

Sequence in context: A038690 A154801 A253094 * A107825 A201332 A049253

Adjacent sequences:  A217012 A217013 A217014 * A217016 A217017 A217018

KEYWORD

nonn,easy

AUTHOR

Alex Ratushnyak, Sep 23 2012

STATUS

approved

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Last modified April 11 15:49 EDT 2021. Contains 342886 sequences. (Running on oeis4.)