Number of Dyck paths of semilength n such that each level has exactly four peaks or no peaks.

Terms

a(0) =1a(1) =0a(2) =0a(3) =0a(4) =1a(5) =1a(6) =4a(7) =7a(8) =11a(9) =22a(10) =81a(11) =235a(12) =673a(13) =2063a(14) =5716a(15) =13627a(16) =33752a(17) =95729a(18) =298232a(19) =946563a(20) =2977953a(21) =9147328a(22) =27004159a(23) =76880498a(24) =217826819a(25) =637089405a(26) =1949908577a(27) =6160707450a(28) =19627448025a(29) =61909478550