Number of n-step spirals on hexagonal lattice.

Terms

a(0) =1a(1) =3a(2) =8a(3) =20a(4) =47a(5) =106a(6) =230a(7) =479a(8) =973a(9) =1924a(10) =3712a(11) =7021a(12) =13034a(13) =23780a(14) =42732a(15) =75703a(16) =132360a(17) =228664a(18) =390611a(19) =660296a(20) =1105321a(21) =1833358a(22) =3014694a(23) =4917036a(24) =7958127a(25) =12786252a(26) =20401469a(27) =32337878a(28) =50936233a(29) =79750436