Number of n-step spirals on hexagonal lattice.

Terms

a(0) =1a(1) =3a(2) =7a(3) =15a(4) =31a(5) =59a(6) =110a(7) =198a(8) =347a(9) =592a(10) =997a(11) =1641a(12) =2666a(13) =4266a(14) =6741a(15) =10525a(16) =16268a(17) =24882a(18) =37717a(19) =56683a(20) =84504a(21) =125031a(22) =183716a(23) =268125a(24) =388873a(25) =560647a(26) =803723a(27) =1146013a(28) =1625731a(29) =2294964