Number of Barlow packings that repeat after exactly n layers.

Terms

a(0) =0a(1) =1a(2) =1a(3) =1a(4) =1a(5) =2a(6) =3a(7) =6a(8) =7a(9) =16a(10) =21a(11) =43a(12) =63a(13) =129a(14) =203a(15) =404a(16) =685a(17) =1343a(18) =2385a(19) =4625a(20) =8492a(21) =16409a(22) =30735a(23) =59290a(24) =112530a(25) =217182a(26) =415620a(27) =803076a(28) =1545463a(29) =2990968