A293060 - OEIS

A293060

Triangle read by rows (n >= 0, 0 <= k <= n): T(n,k) = number of k-dimensional subperiodic groups in n-dimensional space, not counting enantiomorphs.

1, 2, 2, 10, 7, 17, 32, 67, 80, 219, 227, 343, 1076, 1594, 4783, 955

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OFFSET

0,2

COMMENTS

T(n,0) count n-dimensional crystallographic point groups (i.e., left border is A004028), T(n,n) count n-dimensional space groups (i.e., right border is A004029). The name "subperiodic groups" is usually related to the case 0 < k < n only, i.e., symmetry groups of n-dimensional objects including k independent translations which are subgroups of some n-dimensional space groups.

The Bohm symbols for these groups are G_{n,k}, except for the case k=n, when it is G_n.

Some groups have their own names:

T(2,1): frieze groups

T(2,2): wallpaper groups

T(3,1): rod groups

T(3,2): layer groups

See [Palistrant, 2012, p. 476] for row 4.

LINKS

Table of n, a(n) for n=0..15.

M. I. Aroyo et al, Bilbao Crystallographic Server

International Union of Crystallography, International Tables for Crystallography, volumes A and E.

A. F. Palistrant, Complete scheme of four-dimensional crystallographic symmetry groups, Crystallography Reports, 57 (2012), 471-477.