a(n) is the sum of all symmetric valleys in the set of Catalan words of length n.

A371964

a(n) is the sum of all symmetric valleys in the set of Catalan words of length n.

Terms

    a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =7a(6) =35a(7) =155a(8) =650a(9) =2652a(10) =10660a(11) =42484a(12) =168454a(13) =665874a(14) =2627130a(15) =10353290a(16) =40775045a(17) =160534895a(18) =631970495a(19) =2487938015a(20) =9795810125a(21) =38576953505a(22) =151957215305a(23) =598732526105

External references