Number of n-step spirals on hexagonal lattice.

Terms

a(0) =1a(1) =2a(2) =4a(3) =8a(4) =14a(5) =26a(6) =43a(7) =74a(8) =120a(9) =197a(10) =311a(11) =495a(12) =768a(13) =1189a(14) =1811a(15) =2748a(16) =4116a(17) =6136a(18) =9058a(19) =13299a(20) =19370a(21) =28069a(22) =40399a(23) =57856a(24) =82374a(25) =116736a(26) =164574a(27) =231007a(28) =322749a(29) =449089