Number of topologically distinct sets of n circles with one pair intersecting.

Terms

a(0) =1a(1) =4a(2) =15a(3) =50a(4) =162a(5) =506a(6) =1558a(7) =4727a(8) =14227a(9) =42521a(10) =126506a(11) =374969a(12) =1108476a(13) =3269902a(14) =9630631a(15) =28328999a(16) =83251569a(17) =244471484a(18) =717486860a(19) =2104777227a(20) =6172357873a(21) =18096097750a(22) =53044095421a(23) =155464365080a(24) =455601800970