a(n) = n * Clausen(n, 1) / Clausen(n, 0).

Terms

a(0) =0a(1) =2a(2) =6a(3) =2a(4) =60a(5) =2a(6) =42a(7) =2a(8) =120a(9) =6a(10) =66a(11) =2a(12) =5460a(13) =2a(14) =6a(15) =2a(16) =4080a(17) =2a(18) =2394a(19) =2a(20) =660a(21) =2a(22) =138a(23) =2a(24) =10920a(25) =10a(26) =6a(27) =18a(28) =1740a(29) =2