a(n) = Sum_{k=0..floor(n/2)} (C(n+2, k+2) - C(n+2, k)).

Terms

a(0) =0a(1) =2a(2) =5a(3) =14a(4) =28a(5) =62a(6) =117a(7) =242a(8) =451a(9) =912a(10) =1703a(11) =3418a(12) =6420a(13) =12854a(14) =24293a(15) =48602a(16) =92359a(17) =184736a(18) =352695a(19) =705410a(20) =1352055a(21) =2704132a(22) =5200275a(23) =10400574a(24) =20058273a(25) =40116572a(26) =77558731a(27) =155117490a(28) =300540164a(29) =601080358