a(n) = Sum_{k=1..n} binomial(n,k) * floor(n/k).

Terms

a(0) =1a(1) =5a(2) =13a(3) =33a(4) =61a(5) =143a(6) =246a(7) =521a(8) =985a(9) =1995a(10) =3499a(11) =7923a(12) =14028a(13) =28642a(14) =55603a(15) =115369a(16) =210665a(17) =455399a(18) =838338a(19) =1755983a(20) =3383652a(21) =6974159a(22) =13034492a(23) =28011611a(24) =52475486a(25) =108821068a(26) =210050941a(27) =436273458a(28) =824191369a(29) =1744975533