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

Terms

a(0) =1a(1) =5a(2) =31a(3) =195a(4) =1231a(5) =7798a(6) =49596a(7) =316767a(8) =2031535a(9) =13079352a(10) =84504355a(11) =547707394a(12) =3559971156a(13) =23197272140a(14) =151495214536a(15) =991348425879