a(n) = C(n)*(11n+1) where C(n) = Catalan numbers (A000108).

Terms

a(0) =1a(1) =12a(2) =46a(3) =170a(4) =630a(5) =2352a(6) =8844a(7) =33462a(8) =127270a(9) =486200a(10) =1864356a(11) =7171892a(12) =27665596a(13) =106977600a(14) =414538200a(15) =1609344270a(16) =6258307590a(17) =24373220520a(18) =95050101300a(19) =371125269900