Number of permutations of [n] with 4 sequences.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =32a(6) =300a(7) =1852a(8) =9576a(9) =45096a(10) =201060a(11) =866324a(12) =3650592a(13) =15154240a(14) =62260380a(15) =253939116a(16) =1030367448a(17) =4165106264a(18) =16790875860a(19) =67553807428a(20) =271383782544