(n-2)-th Catalan number is congruent to 2n/3 mod n.

Terms

a(0) =9a(1) =12a(2) =15a(3) =27a(4) =30a(5) =33a(6) =81a(7) =84a(8) =87a(9) =117a(10) =120a(11) =123a(12) =243a(13) =246a(14) =249a(15) =279a(16) =282a(17) =285a(18) =333a(19) =336a(20) =339a(21) =351a(22) =354a(23) =357a(24) =729a(25) =732a(26) =735a(27) =765a(28) =768a(29) =771