a(n) = (3/(8n-4))*C(4n,n).

Terms

a(0) =3a(1) =7a(2) =33a(3) =195a(4) =1292a(5) =9177a(6) =68310a(7) =525915a(8) =4153380a(9) =33460284a(10) =273904969a(11) =2271800037a(12) =19050406788a(13) =161242554550