A351160 - OEIS

A351160

Number of polyominoes of 2n cells with both diagonal symmetries, for which the 180-degree rotational symmetry has an axis that coincides with a vertex of a square, but without 90-degree rotational symmetry.

%I #18 Dec 20 2024 12:57:57

%S 0,0,0,1,1,2,4,10,14,37,55,142,208,531,792,2015,3029,7621

%N Number of polyominoes of 2n cells with both diagonal symmetries, for which the 180-degree rotational symmetry has an axis that coincides with a vertex of a square, but without 90-degree rotational symmetry.

%C This sequence enumerates a subset of the polyominoes enumerated by A056878.

%F a(n) = A056878(2*n) - A351159(2*n).

%e a(4)=1 because of:

%e O

%e OOO

%e O

%Y Cf. A000105, A056878, A351159.

%K nonn,more

%O 1,6

%A _John Mason_, Feb 03 2022

%E a(17)-a(18) from _John Mason_, Dec 17 2024