a(n) = A002703(n)/2.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =3a(5) =7a(6) =12a(7) =23a(8) =44a(9) =81a(10) =150a(11) =281a(12) =528a(13) =991a(14) =1871a(15) =3541a(16) =6719a(17) =12787a(18) =24384a(19) =46599a(20) =89240a(21) =171196a(22) =328959a(23) =633101a(24) =1220159a(25) =2354687a(26) =4549752a(27) =8801161a(28) =17043505a(29) =33038207