Number of outerplanar graphs on n unlabeled nodes.

Terms

a(0) =1a(1) =2a(2) =4a(3) =10a(4) =25a(5) =80a(6) =277a(7) =1150a(8) =5291a(9) =26918a(10) =145744a(11) =828856a(12) =4872771a(13) =29395784a(14) =180857382a(15) =1130700488a(16) =7163245811a(17) =45895629266a(18) =296937363511