A171011 - OEIS

%I #6 Apr 29 2016 20:09:37

%S 0,0,1,9,48,242,1178,5793,27651,131383

%N Number of ways to place two non-attacking rooks on all free n-ominoes.

%e The triomino XX admits 1 combination of 2 non-attacking rooks.

%e ............ X

%K nonn

%O 1,4

%A _David Scambler_, Aug 27 2010