Number of loopless rooted planar maps with 4 faces and n vertices and no isthmuses.

Terms

a(0) =1a(1) =20a(2) =131a(3) =469a(4) =1262a(5) =2862a(6) =5780a(7) =10725a(8) =18647a(9) =30784a(10) =48713a(11) =74405a(12) =110284a(13) =159290a(14) =224946a(15) =311429a(16) =423645a(17) =567308a(18) =749023a(19) =976373a(20) =1258010a(21) =1603750a(22) =2024672a(23) =2533221a(24) =3143315a(25) =3870456a(26) =4731845a(27) =5746501a(28) =6935384a(29) =8321522