Largest prime < n-th Catalan number.

Terms

a(0) =3a(1) =13a(2) =41a(3) =131a(4) =421a(5) =1429a(6) =4861a(7) =16787a(8) =58771a(9) =208009a(10) =742897a(11) =2674429a(12) =9694843a(13) =35357657a(14) =129644783a(15) =477638699a(16) =1767263171a(17) =6564120403a(18) =24466266973a(19) =91482563633a(20) =343059613639