The number of permutations of length n that can be sorted by 3 block transpositions.

Terms

a(0) =1a(1) =2a(2) =6a(3) =24a(4) =120a(5) =675a(6) =3527a(7) =15484a(8) =56917a(9) =179719a(10) =500864a(11) =1260117a(12) =2913132a(13) =6274230a(14) =12726573a(15) =24521243a(16) =45190897a(17) =80108200a(18) =137224138a(19) =228026582a(20) =368765112a(21) =581994117a(22) =898492563a(23) =1359625566a(24) =2020220021a(25) =2952034021a(26) =4247907652a(27) =6026690971a(28) =8439053564