Number of Barlow packings with group P3m1 that repeat after n layers.

Terms

a(0) =3a(1) =2a(2) =10a(3) =15a(4) =42a(5) =68a(6) =162a(7) =280a(8) =600a(9) =1088a(10) =2214a(11) =4112a(12) =8154a(13) =15366a(14) =30052a(15) =57208a(16) =111166a(17) =212982a(18) =412890a(19) =794688a(20) =1540002a(21) =2974150a(22) =5767344a(23) =11167872a(24) =21680832a(25) =42073640a(26) =81787057a(27) =159005154a(28) =309503502a(29) =602667098