a(n) = Sum_{k=0..n} (k+1) * A026736(n,n-k).

Terms

a(0) =1a(1) =3a(2) =8a(3) =20a(4) =52a(5) =121a(6) =301a(7) =675a(8) =1628a(9) =3570a(10) =8426a(11) =18202a(12) =42288a(13) =90374a(14) =207464a(15) =439800a(16) =1000194a(17) =2106961a(18) =4755715a(19) =9967599a(20) =22359788a(21) =46670273a(22) =104154703a(23) =216643945a(24) =481381746a(25) =998346275a(26) =2210037191a(27) =4571884119a(28) =10088030640