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 A214250 Sum of the eight nearest neighbors of n in a triangular "horizontal-first" spiral with positive integers. 4
 56, 80, 108, 84, 132, 92, 84, 96, 128, 200, 152, 144, 236, 160, 172, 204, 284, 212, 188, 184, 192, 200, 208, 232, 280, 384, 304, 280, 280, 288, 428, 304, 312, 320, 340, 388, 500, 396, 356, 344, 352, 360, 368, 376, 384, 392, 400, 432, 496, 632, 520, 480, 472, 480 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS EXAMPLE Spiral begins: __ __ __ __ __ __ __ 57 __ __ __ __ __ __ 56 31 58 __ __ __ __ __ 55 30 13 32 59 __ __ __ __ 54 29 12  3 14 33 60 __ __ __ 53 28 11  2  1  4 15 34 61 __ __ 52 27 10  9  8  7  6  5 16 35 62 __ 51 26 25 24 23 22 21 20 19 18 17 36 63 50 49 48 47 46 45 44 43 42 41 40 39 38 37 64 The eight nearest neighbors of 4 are: 1, 3, 14, 33, 15, 5, 6, 7. Their sum is a(4)=84. PROG (Python) SIZE=29  # must be odd grid = [0] * (SIZE*SIZE) saveX = [0]* (SIZE*SIZE) saveY = [0]* (SIZE*SIZE) saveX[1] = saveY[1] = posX = posY = SIZE//2 grid[posY*SIZE+posX]=1 n = 2 def walk(stepX, stepY, chkX, chkY, chkX2, chkY2):   global posX, posY, n   while 1:     posX+=stepX     posY+=stepY     grid[posY*SIZE+posX]=n     saveX[n]=posX     saveY[n]=posY     n+=1     if posX==0 or grid[(posY+chkY)*SIZE+posX+chkX]+grid[(posY+chkY2)*SIZE+posX+chkX2]==0:         return while 1:     walk(-1, 0,  1, -1, 0, -1)   # left     if posX==0:         break     walk( 1, -1,  1, 1,  1, 1)    # right+up     walk( 1, 1, -1,  0, -1, 0)   # right+down for n in range(1, 122):     posX = saveX[n]     posY = saveY[n]     k = grid[(posY-1)*SIZE+posX] + grid[(posY+1)*SIZE+posX]     k+= grid[(posY-1)*SIZE+posX-1] + grid[(posY-1)*SIZE+posX+1]     k+= grid[(posY+1)*SIZE+posX-1] + grid[(posY+1)*SIZE+posX+1]     k+= grid[posY*SIZE+posX-1] + grid[posY*SIZE+posX+1]     print k, CROSSREFS Cf. A214226 - same sum in a triangular "horizontal-last" spiral. Sequence in context: A039335 A043938 A328165 * A286981 A254369 A234927 Adjacent sequences:  A214247 A214248 A214249 * A214251 A214252 A214253 KEYWORD nonn,easy AUTHOR Alex Ratushnyak, Jul 08 2012 STATUS approved

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Last modified September 27 03:21 EDT 2020. Contains 337380 sequences. (Running on oeis4.)