A357647 a(n) is the number of free unholey polyominoes of n cells with 90-degree rotational symmetry and no other.
0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 2, 2, 0, 0, 7, 7, 0, 0, 22, 24, 0, 0, 71, 82, 0, 0, 239, 280, 0, 0, 817, 970, 0, 0, 2841, 3403, 0, 0, 10027, 12064, 0, 0, 35800, 43193, 0, 0, 129007, 156011, 0, 0, 468541, 567664, 0, 0, 1713174
Offset: 1