Number of mirror-symmetrical edge-rooted tree-like octagonal systems.

Terms

a(0) =1a(1) =1a(2) =3a(3) =4a(4) =15a(5) =23a(6) =94a(7) =155a(8) =661a(9) =1139a(10) =4983a(11) =8844a(12) =39362a(13) =71360a(14) =321561a(15) =592361a(16) =2694421a(17) =5025849a(18) =23029195a(19) =43388208a(20) =199990961a(21) =379900479a(22) =1759636142a(23) =3365582261a(24) =15652514944a(25) =30112397278a(26) =140531706444a(27) =271707661708