Squarefree k > 1 with sigma(sigma(sigma(k))) < 3*k + 1.

Terms

a(0) =3a(1) =97a(2) =217a(3) =241a(4) =337a(5) =577a(6) =889a(7) =1249a(8) =1393a(9) =1501a(10) =3361a(11) =3697a(12) =3937a(13) =4039a(14) =4801a(15) =5587a(16) =6961a(17) =7471a(18) =8191a(19) =9481a(20) =10657a(21) =14449a(22) =16177a(23) =16561a(24) =17887a(25) =18049a(26) =18157a(27) =22459a(28) =23527a(29) =23761