Number of achiral 2-connected planar maps with n edges.

Terms

a(0) =0a(1) =1a(2) =2a(3) =3a(4) =6a(5) =14a(6) =30a(7) =77a(8) =196a(9) =525a(10) =1414a(11) =3960a(12) =11056a(13) =31636a(14) =90818a(15) =264657a(16) =774146a(17) =2289787a(18) =6798562a(19) =20354005a(20) =61164374a(21) =184985060a(22) =561433922a(23) =1712696708a(24) =5241637812