Numbers k such that phi(k) | sigma_2(k).

Terms

a(0) =1a(1) =2a(2) =3a(3) =6a(4) =22a(5) =33a(6) =66a(7) =750a(8) =27798250a(9) =41697375a(10) =76745867a(11) =83394750a(12) =153491734a(13) =207656250a(14) =230237601a(15) =460475202a(16) =917342250a(17) =969062500a(18) =2907187500a(19) =4528006153a(20) =5952812500a(21) =9056012306a(22) =13584018459a(23) =17858437500a(24) =27168036918a(25) =31979062500a(26) =57559400250