Numbers k such that sigma(k) divides sigma(sigma(k)).

Terms

a(0) =1a(1) =5a(2) =12a(3) =54a(4) =56a(5) =87a(6) =95a(7) =276a(8) =308a(9) =427a(10) =429a(11) =446a(12) =455a(13) =501a(14) =581a(15) =611a(16) =9120a(17) =9180a(18) =9504a(19) =9720a(20) =9960a(21) =10296a(22) =10620a(23) =10740a(24) =10824a(25) =11070a(26) =11310a(27) =11480a(28) =11484a(29) =11556