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 A214226 Sum of the eight nearest neighbors of n in a triangular horizontal-last spiral with positive integers. 6
 72, 80, 60, 76, 132, 100, 164, 112, 136, 200, 144, 128, 128, 136, 156, 196, 284, 220, 204, 208, 324, 224, 232, 248, 288, 384, 296, 264, 256, 264, 272, 280, 288, 296, 324, 380, 500, 404, 372, 368, 376, 384, 548, 400, 408, 416, 424, 448, 504, 632, 512, 464, 448 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS EXAMPLE Triangular spiral begins: __ __ __ __ __ __ __ 43 __ __ __ __ __ __ 42 21 44 __ __ __ __ __ 41 20  7 22 45 __ __ __ __ 40 19  6  1  8 23 46 __ __ __ 39 18  5  4  3  2  9 24 47 __ __ 38 17 16 15 14 13 12 11 10 25 48 __ 37 36 35 34 33 32 31 30 29 28 27 26 49 64 63 62 61 60 69 58 57 56 55 54 53 52 51 50 The eight nearest neighbors of 3 are 6, 1, 8, 4, 2, 14, 13, 12; their sum is a(3)=60. PROG (Python) SIZE=27 # 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, 1, -1,  0, -1, 0)    # right+down     walk(-1, 0,  1, -1, 0, -1)    # left     if posX==0:         break     walk( 1, -1,  1, 1, 1, 1)    # right+up for n in range(1, 101):     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. A002061 - numbers on the central vertical axis. Cf. A054552 - numbers on the axis starting with 1 and 2. Cf. A214227 - sum of the four nearest neighbors. Cf. A214250 - same sum in a triangular "horizontal-first" spiral. Sequence in context: A138691 A039670 A065147 * A043187 A039364 A043967 Adjacent sequences:  A214223 A214224 A214225 * A214227 A214228 A214229 KEYWORD nonn,easy AUTHOR Alex Ratushnyak, Jul 07 2012 STATUS approved

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Last modified August 9 12:53 EDT 2022. Contains 356026 sequences. (Running on oeis4.)