a(n) = phi(lcm(1,2,3,...,n)), where phi is Euler's totient function.

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =16a(5) =16a(6) =96a(7) =192a(8) =576a(9) =576a(10) =5760a(11) =5760a(12) =69120a(13) =69120a(14) =69120a(15) =138240a(16) =2211840a(17) =2211840a(18) =39813120a(19) =39813120a(20) =39813120a(21) =39813120a(22) =875888640a(23) =875888640a(24) =4379443200a(25) =4379443200a(26) =13138329600a(27) =13138329600a(28) =367873228800a(29) =367873228800