Number of ways two dihexes can be placed on an n-th regular hexagonal board.

Terms

a(0) =0a(1) =33a(2) =702a(3) =3630a(4) =11409a(5) =27603a(6) =56748a(7) =104352a(8) =176895a(9) =281829a(10) =427578a(11) =623538a(12) =880077a(13) =1208535a(14) =1621224a(15) =2131428a(16) =2753403a(17) =3502377a(18) =4394550a(19) =5447094a(20) =6678153a(21) =8106843a(22) =9753252a(23) =11638440a(24) =13784439a(25) =16214253a(26) =18951858a(27) =22022202a(28) =25451205a(29) =29265759