Number of permutations with certain forbidden subsequences.

Terms

a(0) =1a(1) =1a(2) =2a(3) =5a(4) =14a(5) =42a(6) =131a(7) =418a(8) =1352a(9) =4410a(10) =14463a(11) =47605a(12) =157084a(13) =519255a(14) =1718653a(15) =5693903a(16) =18877509a(17) =62620857a(18) =207816230a(19) =689899944a(20) =2290913666a(21) =7608939443a(22) =25276349558a(23) =83977959853a(24) =279039638062a(25) =927272169336