A190827 Number of permutations of 3 copies of 1..n introduced in order 1..n with no element equal to another within a distance of 2

0, 0, 1, 109, 12721, 2001240, 418539642, 113320421342, 38733396860601, 16350175635962731

Offset

1,4

Links

Table of n, a(n) for n=1..10.

Example

Some solutions for n=4
..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
..1....4....4....1....4....4....4....4....4....4....4....1....4....4....4....4
..4....2....1....4....2....1....2....2....2....1....2....4....2....2....1....2
..2....1....2....3....1....2....1....3....3....2....3....3....1....1....2....3
..3....3....4....2....3....4....4....1....4....3....1....2....4....3....4....4
..4....2....1....1....4....3....3....4....1....4....4....4....3....4....3....1
..1....4....3....4....1....1....2....3....3....2....2....1....1....1....1....2
..2....1....2....2....2....4....1....2....4....1....3....3....2....2....2....4
..4....3....4....3....4....3....4....4....2....3....1....4....3....3....4....3
..3....4....3....4....3....2....3....1....1....4....4....2....4....4....3....1

Crossrefs

Sequence in context: A357231 A227949 A144930 * A125044 A352466 A096209

Adjacent sequences: A190824 A190825 A190826 * A190828 A190829 A190830

Keyword

nonn

Author

R. H. Hardin May 21 2011

Status

approved