Kekulé numbers for certain benzenoids.

Terms

a(0) =3a(1) =20a(2) =136a(3) =928a(4) =6336a(5) =43264a(6) =295424a(7) =2017280a(8) =13774848a(9) =94060544a(10) =642285568a(11) =4385800192a(12) =29948116992a(13) =204498534400