a(n) = gcd(Phi(n!), Phi(n^n), Phi(lcm(1..n))).

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =4a(5) =16a(6) =6a(7) =64a(8) =18a(9) =64a(10) =10a(11) =1152a(12) =12a(13) =1536a(14) =1080a(15) =1024a(16) =16a(17) =442368a(18) =18a(19) =163840a(20) =972a(21) =163840a(22) =22a(23) =15925248a(24) =100a(25) =196608a(26) =1458a(27) =196608a(28) =28a(29) =4777574400