Number of Barlow packings with group P3(bar)m1(S) that repeat after 2n layers.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =2a(5) =3a(6) =9a(7) =16a(8) =39a(9) =75a(10) =165a(11) =318a(12) =672a(13) =1323a(14) =2703a(15) =5376a(16) =10880a(17) =21663a(18) =43605a(19) =87040a(20) =174564a(21) =348843a(22) =698709a(23) =1396680a(24) =2795518a(25) =5589675a(26) =11183325a(27) =22364160a(28) =44736512a(29) =89467320