A189839 Number of ways to place n nonattacking composite pieces rook + rider[3,3] on an n X n chessboard.

1, 2, 6, 20, 80, 384, 2112, 12992, 94272, 716800, 6141440, 58451568, 596647568, 6555879072, 77766001056, 981202169600

Offset

1,2

Comments

a(n) is also number of permutations p of 1,2,...,n satisfying |p(j+3k)-p(j)|<>3k for all j>=1, k>=1, j+3k<=n

Links

Table of n, a(n) for n=1..16.

V. Kotesovec, Number of ways of placing non-attacking queens, kings, bishops and knights (in English and Czech)

Wikipedia, Fairy chess piece

Crossrefs

Cf. A117574, A000170, A189838

Sequence in context: A186365 A245373 A204440 * A117574 A177481 A177475

Adjacent sequences: A189836 A189837 A189838 * A189840 A189841 A189842

Keyword

nonn,hard

Author

Vaclav Kotesovec, Apr 29 2011

Status

approved