Numbers k such that k*sigma(k)*sigma(sigma(k)) is a square.

Terms

a(0) =1a(1) =42a(2) =234a(3) =2430a(4) =3510a(5) =3724a(6) =6750a(7) =49005a(8) =72618a(9) =165726a(10) =167580a(11) =318091a(12) =412776a(13) =510489a(14) =642096a(15) =771875a(16) =816998a(17) =859740a(18) =1003275a(19) =1073452a(20) =1166719a(21) =1368576a(22) =1604645a(23) =1712256a(24) =1984500a(25) =2297762a(26) =2500875a(27) =2735810a(28) =2852928a(29) =3082950