A190927 Number of permutations of n copies of 1..7 introduced in order 1..7 with no element equal to another within a distance of 1.

1, 47844, 4420321081, 551248360550999, 81644850343968535401, 13519747358522016160671387, 2421032324142610480402567434373, 459408385876250801291447710561829082, 91155245844064069307740171414201519055298

Offset: 1

Author

R. H. Hardin, May 23 2011

Keywords

• nonn

Examples

			Some solutions for n=2:
  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1
  2  2  2  2  2  2  2  2  2  2  2  2  2  2  2  2
  3  3  3  3  3  3  3  3  3  3  3  3  3  3  3  3
  4  4  4  4  4  2  2  4  4  4  2  4  4  4  4  2
  5  5  5  1  5  4  4  2  5  5  4  2  1  3  2  1
  6  6  6  5  6  5  3  5  3  6  5  4  4  5  5  4
  2  7  4  6  7  6  5  6  6  3  6  5  5  6  6  5
  7  3  5  4  2  3  6  5  7  7  7  1  6  4  4  6
  5  4  2  2  1  5  7  6  2  6  3  6  7  5  7  7
  6  5  6  3  6  4  5  1  4  1  7  3  2  7  1  3
  4  6  1  5  7  7  7  3  7  7  5  7  5  2  7  4
  3  2  7  7  5  1  1  7  1  5  1  6  7  1  5  6
  7  7  3  6  4  6  6  4  5  4  6  5  6  7  6  7
  1  1  7  7  3  7  4  7  6  2  4  7  3  6  3  5
		

Links

• Seiichi Manyama, Table of n, a(n) for n = 1..185 (terms 1..25 from R. H. Hardin)

Crossrefs

Column k=7 of A322013.

Cf. A000012 (b=2), A190917 (b=3), A190918 (b=4), A190920 (b=5), A190923 (b=6), A190932 (b=8), A321987 (b=9).

Formula

a(n) ~ 343 * sqrt(7) * 2^(7*n-8) * 3^(7*n-3) / (625 * Pi^3 * n^3). - Vaclav Kotesovec, Nov 24 2018