A189844 Number of ways to place n nonattacking composite pieces rook + semi-rider[3,3] on an n X n chessboard.

1, 2, 6, 22, 98, 534, 3334, 23724, 191820, 1704532, 16689868, 179288892, 2069311996, 25760882744, 345073745880, 4900331447624

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.

For information about semi-pieces see semi-bishop (A187235) and semi-queen (A099152).

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. A189282, A099152, A189843, A189839, A187235

Sequence in context: A130907 A054096 A006183 * A189282 A318974 A012269

Adjacent sequences: A189841 A189842 A189843 * A189845 A189846 A189847

Keyword

nonn,hard

Author

Vaclav Kotesovec, Apr 29 2011

Status

approved