Indices of (-1)sigma perfect numbers.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =2a(6) =2a(7) =2a(8) =1a(9) =1a(10) =2a(11) =1a(12) =2a(13) =2a(14) =2a(15) =2a(16) =2a(17) =3