Number of close-packings with layer-number 3n and space group R3m.

Terms

a(0) =1a(1) =2a(2) =4a(3) =10a(4) =21a(5) =42a(6) =84a(7) =164a(8) =322a(9) =620a(10) =1200a(11) =2300a(12) =4429a(13) =8482a(14) =16303a(15) =31259a(16) =60105a(17) =115472a(18) =222332a(19) =428106a(20) =825774a(21) =1593669a(22) =3080004a(23) =5956902a(24) =11534689a(25) =22352962a(26) =43361663a(27) =84181720a(28) =163574114a(29) =318079104