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Related to class numbers of cyclotomic fields, although the precise relationship is not clear to me. Compare A000927.
Mermin, N. David; Rokhsar, Daniel S.; and Wright, David C.; Beware of 46-fold symmetry: the classification of two-dimensional quasicrystallographic lattices. Phys. Rev. Lett. 58 (1987), 2099-2101.
Table of n, a(n) for n=2..49.
See A193175 for values of 2n such that a(n) = 1.
Sequence in context: A083985 A109848 A104146 * A133705 A046111 A131779
Adjacent sequences: A193176 A193177 A193178 * A193180 A193181 A193182
N. J. A. Sloane, Jul 17 2011