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

6,3

Links

Table of n, a(n) for n=6..43.

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.

Sequence in context: A005509 A147366 A056318 * A256216 A285462 A146387

Adjacent sequences: A011945 A011946 A011947 * A011949 A011950 A011951

Keyword

nonn

Author

N. J. A. Sloane

Status

approved