Number of permutations of length n which avoid the patterns 321, 31245.

Terms

a(0) =1a(1) =2a(2) =5a(3) =14a(4) =41a(5) =116a(6) =307a(7) =760a(8) =1779a(9) =3986a(10) =8641a(11) =18282a(12) =38005a(13) =78024a(14) =158791a(15) =321236a(16) =647247a(17) =1300630a(18) =2609029a(19) =5227766a(20) =10467521a(21) =20949692a(22) =41917115a(23) =83855504a(24) =167736331a(25) =335502586a(26) =671040297a(27) =1342121570a(28) =2684290669a(29) =5368636176