A327734 Number of n-bead bracelet structures using exactly two different colored beads that are not self-equivalent under either a nonzero rotation or reversal (turning over bracelet).
0, 0, 0, 0, 0, 0, 1, 2, 7, 12, 31, 57, 126, 232, 484, 900, 1800, 3388, 6643, 12594, 24457, 46624, 90157, 172680, 333498, 641088, 1238664, 2388357, 4620006, 8931052
Offset: 1
Examples
Case n=7: There are 7 necklace structures using exactly two colors. See example in A056295. Of these, 5 are achiral and the other two a chiral pair: AAABABB/AAABBAB. a(7) = 1, since this sequence considers chiral pairs as the same bracelet structure.