Number of diagonal dissections of an n-gon into 3 regions.

Terms

a(0) =0a(1) =5a(2) =21a(3) =56a(4) =120a(5) =225a(6) =385a(7) =616a(8) =936a(9) =1365a(10) =1925a(11) =2640a(12) =3536a(13) =4641a(14) =5985a(15) =7600a(16) =9520a(17) =11781a(18) =14421a(19) =17480a(20) =21000a(21) =25025a(22) =29601a(23) =34776a(24) =40600a(25) =47125a(26) =54405a(27) =62496a(28) =71456a(29) =81345