A217212 Number of sequences of 2's and 3's of length n with curling number 3.
0, 0, 2, 2, 4, 10, 20, 38, 82, 164, 328, 660, 1320, 2640, 5304, 10596, 21192, 42424, 84848, 169668, 339428, 678856, 1357712, 2715548, 5431096, 10862192, 21724746, 43449380, 86898760, 173798220, 347596440, 695192670
Offset: 1