Number of Barlow packings with group R3(bar)m(O) that repeat after 6n layers.

Terms

a(0) =1a(1) =2a(2) =4a(3) =9a(4) =19a(5) =40a(6) =80a(7) =165a(8) =330a(9) =672a(10) =1344a(11) =2709a(12) =5418a(13) =10878a(14) =21760a(15) =43605a(16) =87211a(17) =174592a(18) =349180a(19) =698707a(20) =1397418a(21) =2795520a(22) =5591040a(23) =11183436a(24) =22366890a(25) =44736512a(26) =89473020a(27) =178951509a(28) =357903000a(29) =715816960