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A217012 Permutation of natural numbers arising from applying the walk of a square spiral (e.g. A214526) to the data of right triangular type-3 spiral (defined in A214252). 2
1, 8, 25, 9, 2, 3, 4, 5, 6, 7, 24, 50, 85, 51, 26, 10, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 23, 49, 84, 128, 181, 129, 86, 52, 27, 11, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 22, 48, 83, 127, 180, 242 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..56.

PROG

(Python)

SIZE = 33       # must be 4k+1

grid = [0] * (SIZE*SIZE)

posX = posY = SIZE//2

grid[posY*SIZE+posX]=1

n = 2

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 posY!=0:

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

    walk(-1, 0,  0, -1)    # left

    walk(0, -1,  1,  1)    # up

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, A214252, A217010.

Sequence in context: A076444 A023056 A103954 * A200838 A302160 A122984

Adjacent sequences:  A217009 A217010 A217011 * A217013 A217014 A217015

KEYWORD

nonn,easy

AUTHOR

Alex Ratushnyak, Sep 23 2012

STATUS

approved

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Last modified April 19 20:40 EDT 2019. Contains 322291 sequences. (Running on oeis4.)