Number of Dyck paths of length 2n with exactly 2 hills.

Terms

a(0) =0a(1) =0a(2) =1a(3) =0a(4) =3a(5) =6a(6) =21a(7) =66a(8) =220a(9) =744a(10) =2562a(11) =8942a(12) =31569a(13) =112530a(14) =404445a(15) =1464042a(16) =5332872a(17) =19532688a(18) =71893470a(19) =265778040a(20) =986416614a(21) =3674092044a(22) =13729259586a(23) =51455182260a(24) =193369903608a(25) =728504292576