Number of 1-2-3-avoiding permutations with exactly thrice the 1-3-2 pattern.

Terms

a(0) =1a(1) =5a(2) =18a(3) =57a(4) =168a(5) =472a(6) =1280a(7) =3376a(8) =8704a(9) =22016a(10) =54784a(11) =134400a(12) =325632a(13) =780288a(14) =1851392a(15) =4354048a(16) =10158080a(17) =23527424a(18) =54132736a(19) =123797504a(20) =281542656a(21) =637009920a(22) =1434451968a(23) =3215982592a(24) =7180648448a(25) =15971909632a(26) =35399925760a(27) =78198603776a(28) =172201345024