Number of connected relations.

Terms

a(0) =1a(1) =21a(2) =265a(3) =2733a(4) =25441a(5) =223461a(6) =1895545a(7) =15736413a(8) =128882641a(9) =1046542101a(10) =8451838825a(11) =68020609293a(12) =546227922241