The number of squarefree permutations of 1,...,n.

Terms

a(0) =1a(1) =2a(2) =6a(3) =12a(4) =34a(5) =104a(6) =406a(7) =1112a(8) =3980a(9) =15216a(10) =68034a(11) =312048a(12) =1625968a(13) =8771376a(14) =53270068a(15) =319218912a(16) =2135312542a(17) =14420106264a(18) =109051882344a(19) =815868128288