Number of graphs with n nodes having fewer than n edges.

Terms

a(0) =1a(1) =2a(2) =3a(3) =7a(4) =14a(5) =33a(6) =81a(7) =215a(8) =601a(9) =1808a(10) =5721a(11) =19133a(12) =67218a(13) =247377a(14) =950679a(15) =3806360a(16) =15837196a(17) =68336348a(18) =305196782a(19) =1408294018a(20) =6703197359a(21) =32861879994a(22) =165699114887a(23) =858237346563