A189843 Number of ways to place n nonattacking composite pieces rook + semi-rider[2,2] on an n X n chessboard.

1, 2, 5, 18, 71, 356, 2097, 14212, 105821, 887576, 8093601, 81310936, 876456695, 10257217440, 127631146697, 1705775408656

Offset

1,2

Comments

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

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. A189281, A099152, A189838, A187235

Sequence in context: A365120 A268570 A141494 * A045612 A371494 A103940

Adjacent sequences: A189840 A189841 A189842 * A189844 A189845 A189846

Keyword

nonn,hard

Author

Vaclav Kotesovec, Apr 29 2011

Status

approved