Number of Barlow packings with group P3(bar)m1(SO) that repeat after 2n-1 layers.

Terms

a(0) =0a(1) =0a(2) =1a(3) =3a(4) =3a(5) =11a(6) =21a(7) =39a(8) =85a(9) =171a(10) =333a(11) =683a(12) =1364a(13) =2715a(14) =5461a(15) =10923a(16) =21813a(17) =43687a(18) =87381a(19) =174699a(20) =349525a(21) =699051a(22) =1397970a(23) =2796203a(24) =5592402a(25) =11184555a(26) =22369621a(27) =44739231a(28) =89477973a(29) =178956971