A011948 Number of Barlow packings with group P63mc that repeat after 2n layers.

1, 1, 4, 7, 18, 31, 70, 126, 261, 484, 960, 1800, 3514, 6643, 12852, 24457, 47151, 90157, 173740, 333498, 643230, 1238664, 2392650, 4620006, 8939657, 17302033, 33538048, 65042495, 126289800, 245361171, 477153040, 928510506, 1808276211, 3523813566, 6871685532, 13408154100, 26178323928, 51139027135

Offset: 6

Author

N. J. A. Sloane

Keywords

• nonn

Links

• D. Bundala, M. Codish, L. Cruz-Filipe et al., Optimal-Depth Sorting Networks, arXiv preprint arXiv:1412.5302 [cs.DS], 2014. (See Table 4)
• J. E. Iglesias, Enumeration of closest-packings by the space group: a simple approach, Z. Krist. 221 (2006) 237-245, Table 3.
• T. J. McLarnan, The numbers of polytypes in close-packings and related structures, Zeits. Krist. 155, 269-291 (1981).

Crossrefs

Appears to be column k=2 of A309784.

Cf. A045668.