a(n) = Sum_{i=0..n} binomial(2n+i,2i).

Terms

a(0) =1a(1) =4a(2) =26a(3) =176a(4) =1204a(5) =8273a(6) =56967a(7) =392688a(8) =2708322a(9) =18683233a(10) =128892764a(11) =889172365a(12) =6133354976a(13) =42300883471a(14) =291696384929