a(n) is the number of permutations p of [n] such that lcm(i, p(i)) <= n for all i in [n].

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =8a(5) =10a(6) =56a(7) =64a(8) =192a(9) =332a(10) =1184a(11) =1264a(12) =12192a(13) =12872a(14) =37568a(15) =100836a(16) =311760a(17) =322320a(18) =2338368a(19) =2408848a(20) =14433408a(21) =32058912a(22) =76931008a(23) =78528704a(24) =919469408a(25) =1158792224a(26) =2689828672a(27) =4675217824a(28) =21679173184a(29) =21984820864