a(n) = lcm{ phi(1), ..., phi(n) }, where phi is Euler's totient function A000010.

Terms

a(0) =1a(1) =1a(2) =2a(3) =2a(4) =4a(5) =4a(6) =12a(7) =12a(8) =12a(9) =12a(10) =60a(11) =60a(12) =60a(13) =60a(14) =120a(15) =120a(16) =240a(17) =240a(18) =720a(19) =720a(20) =720a(21) =720a(22) =7920a(23) =7920a(24) =7920a(25) =7920a(26) =7920a(27) =7920a(28) =55440a(29) =55440