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

A372878

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

Terms

    a(0) =1a(1) =7a(2) =33a(3) =133a(4) =496a(5) =1770a(6) =6142a(7) =20902a(8) =70107a(9) =232489a(10) =763927a(11) =2491107a(12) =8071234a(13) =26007364a(14) =83402988a(15) =266351548a(16) =847482277a(17) =2687729595a(18) =8499036925a(19) =26804655025a(20) =84336597636a(21) =264777690382a(22) =829636763338

External references