Number of achiral planar maps with n edges.

Terms

a(0) =1a(1) =2a(2) =4a(3) =14a(4) =47a(5) =184a(6) =761a(7) =3314a(8) =14997a(9) =69886a(10) =333884a(11) =1626998a(12) =8067786a(13) =40580084a(14) =206734083a(15) =1064666724a(16) =5536480877a(17) =29036188788a(18) =153450351924a(19) =816503772830