a(n) is the least number k > 0 such that sigma(k/n) = phi(k).

Terms

a(0) =1a(1) =2a(2) =45a(3) =12a(4) =70a(5) =36a(6) =42a(7) =336a(8) =270a(9) =420a(10) =1848a(11) =2520a(12) =2730a(13) =5880a(14) =12600a(15) =332640a(16) =353430a(17) =166320a(18) =175560a(19) =1663200a(20) =2522520a(21) =87650640a(22) =118798680a(23) =1051807680a(24) =671517000a(25) =1139458320a(26) =35231316120a(27) =15952416480a(28) =16522145640a(29) =495664369200