Number of permutations of [n+1] avoiding 2413, 3142, 1324, 4231.

Terms

a(0) =1a(1) =2a(2) =6a(3) =20a(4) =64a(5) =194a(6) =562a(7) =1570a(8) =4258a(9) =11266a(10) =29186a(11) =74242a(12) =185858a(13) =458754a(14) =1118210a(15) =2695170a(16) =6430722a(17) =15204354a(18) =35651586a(19) =82968578a(20) =191758338a(21) =440401922a(22) =1005584386a(23) =2283798530a(24) =5161091074a(25) =11609833474a(26) =26004684802a(27) =58015612930a(28) =128949682178