A220102 Permutation of natural numbers arising from applying the walk of square spiral (e.g. A214526) to the data of double square spiral (defined in A220098).

1, 2, 4, 6, 8, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 50, 52, 54, 56

Offset

1,2

Links

Table of n, a(n) for n=1..69.

Prog

(C)
#include <stdio.h>
#define SIZE 20
int grid[SIZE][SIZE];
int direction[] = {0, -1,  1, 0, 0, 1, -1, 0};
main() {
  int i, j, x1, y1, x2, y2, stepSize;
  int direction1pos=0, direction2pos=4, val;
  x1 = y1 = x2 = y2 = SIZE/2;
  for (val=grid[y1][x1]=1, stepSize=0; ; ++stepSize) {
    if (x1<1 || x1>=SIZE-1 || x2<1 || x2>=SIZE-1) break;
    if (y1<1 || y1>=SIZE-1 || y2<1 || y2>=SIZE-1) break;
    for (i=stepSize|1; i; ++val, --i) {
      x1 += direction[direction1pos  ];
      y1 += direction[direction1pos+1];
      x2 += direction[direction2pos  ];
      y2 += direction[direction2pos+1];
      grid[y1][x1] = val*2;
      grid[y2][x2] = val*2+1;
    }
    direction1pos = (direction1pos+2) & 7;
    direction2pos = (direction2pos+2) & 7;
  }
  direction1pos=0;
  x1 = y1 = SIZE/2;
  for (stepSize=2; ; ++stepSize) {
    for (i=stepSize/2; i; --i) {
      if (grid[y1][x1]==0) return;
      printf("%d, ", grid[y1][x1]);
      x1 += direction[direction1pos  ];
      y1 += direction[direction1pos+1];
    }
    direction1pos = (direction1pos+2) & 7;
  }
}

Crossrefs

Cf. A214526, A220098, A217010, A217011, A217012, A217013, A217014, A217015.

Sequence in context: A004093 A106202 A351330 * A308080 A179657 A239887

Adjacent sequences: A220099 A220100 A220101 * A220103 A220104 A220105

Keyword

nonn

Author

Alex Ratushnyak, Dec 04 2012

Status

approved