This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A217293 #9 Mar 04 2025 14:46:52 %S A217293 1,5,6,7,8,9,10,2,4,16,36,17,18,19,20,21,22,23,24,25,26,51,27,11,3,15, %T A217293 35,63,99,64,37,38,39,40,41,42,43,44,45,46,47,48,49,50,83,124,84,52, %U A217293 28,12,14,34,62,98,142,194,143,100,65,66,67,68,69,70,71,72 %N A217293 Permutation of natural numbers arising from applying the walk of right triangular type-3 spiral (defined in A214252) to the data of square spiral (e.g. A214526). %o A217293 (Python) %o A217293 SIZE = 29 # must be 4k+1 %o A217293 grid = [0] * (SIZE*SIZE) %o A217293 posX = posY = SIZE//2 %o A217293 grid[posY*SIZE+posX]=1 %o A217293 n = 2 %o A217293 def walk(stepX, stepY, chkX, chkY): %o A217293 global posX, posY, n %o A217293 while 1: %o A217293 posX+=stepX %o A217293 posY+=stepY %o A217293 grid[posY*SIZE+posX]=n %o A217293 n+=1 %o A217293 if grid[(posY+chkY)*SIZE+posX+chkX]==0: %o A217293 return %o A217293 while posX: %o A217293 walk(0, -1, 1, 0) # up %o A217293 walk(1, 0, 0, 1) # right %o A217293 walk(0, 1, -1, 0) # down %o A217293 walk(-1, 0, 0, -1) # left %o A217293 import sys %o A217293 grid2 = [0] * (SIZE*SIZE) %o A217293 posX = posY = SIZE//2 %o A217293 grid2[posY*SIZE+posX]=1 %o A217293 def walk2(stepX, stepY, chkX, chkY): %o A217293 global posX, posY %o A217293 while 1: %o A217293 a = grid[posY*SIZE+posX] %o A217293 if a==0: %o A217293 sys.exit(1) %o A217293 print(a, end=', ') %o A217293 posX+=stepX %o A217293 posY+=stepY %o A217293 grid2[posY*SIZE+posX]=1 %o A217293 if grid2[(posY+chkY)*SIZE+posX+chkX]==0: %o A217293 return %o A217293 while posY!=0: %o A217293 walk2( 1, 1, -1, 0) # right-down %o A217293 walk2(-1, 0, 0, -1) # left %o A217293 walk2(0, -1, 1, 1) # up %Y A217293 Cf. A214252, A214526, A217012. %K A217293 nonn %O A217293 1,2 %A A217293 _Alex Ratushnyak_, Sep 30 2012