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%I #4 Oct 01 2012 01:50:46
%S 1,5,6,7,22,8,2,4,16,36,17,18,19,20,21,44,75,45,23,9,11,3,15,35,63,99,
%T 64,37,38,39,40,41,42,43,74,113,160,114,76,46,24,10,28,12,14,34,62,98,
%U 142,194,143,100,65,66,67,68,69,70,71,72,73,112,159,214,277
%N Permutation of natural numbers arising from applying the walk of triangular horizontal-last spiral (defined in A214226) to the data of square spiral (e.g. A214526).
%o (Python)
%o SIZE = 29 # must be 4k+1
%o grid = [0] * (SIZE*SIZE)
%o posX = posY = SIZE//2
%o grid[posY*SIZE+posX]=1
%o n = 2
%o def walk(stepX, stepY, chkX, chkY):
%o global posX, posY, n
%o while 1:
%o posX+=stepX
%o posY+=stepY
%o grid[posY*SIZE+posX]=n
%o n+=1
%o if grid[(posY+chkY)*SIZE+posX+chkX]==0:
%o return
%o while posX:
%o walk(0, -1, 1, 0) # up
%o walk(1, 0, 0, 1) # right
%o walk(0, 1, -1, 0) # down
%o walk(-1, 0, 0, -1) # left
%o import sys
%o grid2 = [0] * (SIZE*SIZE)
%o posX = posY = SIZE//2
%o grid2[posY*SIZE+posX]=1
%o def walk2(stepX, stepY, chkX, chkY):
%o global posX, posY
%o while 1:
%o a = grid[posY*SIZE+posX]
%o if a==0:
%o sys.exit(1)
%o print a,
%o posX+=stepX
%o posY+=stepY
%o grid2[posY*SIZE+posX]=1
%o if grid2[(posY+chkY)*SIZE+posX+chkX]==0:
%o return
%o while 1:
%o walk2(1, 1, -1, 0) # down-right
%o walk2(-1, 0, 1, -1) # left
%o walk2(-1, 0, 1, -1) # left
%o if posX<2:
%o break
%o walk2(1, -1, 1, 1) # up-right
%Y Cf. A214226, A214526, A217014.
%K nonn
%O 1,2
%A _Alex Ratushnyak_, Sep 30 2012
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