Nonprime numbers k such that k divides sigma(k^2) - 1.

Terms

a(0) =1a(1) =6a(2) =18a(3) =20a(4) =30a(5) =80a(6) =180a(7) =225a(8) =1968a(9) =5494a(10) =8280a(11) =20820a(12) =37976a(13) =175848a(14) =2635928a(15) =3747827a(16) =15737100a(17) =1162783652a(18) =1453479565a(19) =27961574707a(20) =155176161190