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 A215577 Number of nonintersecting (or self-avoiding) rook paths joining opposite corner cells of an n X n X n grid, avoiding cells that are not on the surface. 0
 1, 18, 340812, 1553113040 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS When n<3 there are n^3 cells available, otherwise n^3 - (n-2)^3. The length of the step is 1. The length of the path varies. LINKS Table of n, a(n) for n=1..4. PROG (C) #include // GCC -O3 char grid[4][4][4]; long long SIZE; long long calc_ways(long long x, long long y, long long z) { long long n; if (grid[x][y][z]) return 0; if (x+y+z==SIZE*3-3) return 1; grid[x][y][z]=1; n=0; if (x>0) n =calc_ways(x-1, y, z); // go left if (x0) n+=calc_ways(x, y-1, z); // down if (y0) n+=calc_ways(x, y, z-1); // level down if (z

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Last modified June 16 08:45 EDT 2024. Contains 373424 sequences. (Running on oeis4.)