a(n) = number of weakly threshold graphs on n nodes.

Terms

a(0) =0a(1) =1a(2) =2a(3) =4a(4) =9a(5) =21a(6) =52a(7) =134a(8) =355a(9) =957a(10) =2608a(11) =7154a(12) =19701a(13) =54379a(14) =150302a(15) =415762a(16) =1150609a(17) =3185147a(18) =8818620a(19) =24418128a(20) =67615743a(21) =187239359a(22) =518506932a(23) =1435875288a(24) =3976322869a(25) =11011542937a(26) =30494088494a(27) =84446895364a(28) =233857897749a(29) =647620493541