sigma(n)-n is a perfect square associated with A049226.

Terms

a(0) =25a(1) =49a(2) =1156a(3) =2809a(4) =1369a(5) =169a(6) =225a(7) =3025a(8) =4489a(9) =5929a(10) =441a(11) =5329a(12) =25281a(13) =10609a(14) =37249a(15) =10609a(16) =27889a(17) =24649a(18) =1225a(19) =22801a(20) =80089a(21) =37249a(22) =85849a(23) =34225a(24) =187489a(25) =1849a(26) =208849a(27) =157609a(28) =76729a(29) =2401