Denominator of Sum_{k=1..n}(-1)^k/phi(k), where phi = A000010.

Terms

a(0) =1a(1) =1a(2) =2a(3) =1a(4) =4a(5) =4a(6) =12a(7) =3a(8) =6a(9) =12a(10) =60a(11) =30a(12) =60a(13) =20a(14) =40a(15) =20a(16) =80a(17) =240a(18) =720a(19) =720a(20) =720a(21) =144a(22) =1584a(23) =1584a(24) =7920a(25) =7920a(26) =7920a(27) =7920a(28) =55440a(29) =55440