Number of counterclockwise n-step spirals on hexagonal lattice where turns of 2*Pi/3 are forbidden.

Terms

a(0) =1a(1) =2a(2) =4a(3) =8a(4) =16a(5) =31a(6) =60a(7) =112a(8) =207a(9) =375a(10) =667a(11) =1173a(12) =2026a(13) =3466a(14) =5846a(15) =9770a(16) =16138a(17) =26441a(18) =42893a(19) =69073a(20) =110309a(21) =174972a(22) =275554a(23) =431286a(24) =670782a(25) =1037412a(26) =1595412a(27) =2440904a(28) =3715497a(29) =5628849