sigma(2*n^2) - sigma(n^2).

Terms

a(0) =2a(1) =8a(2) =26a(3) =32a(4) =62a(5) =104a(6) =114a(7) =128a(8) =242a(9) =248a(10) =266a(11) =416a(12) =366a(13) =456a(14) =806a(15) =512a(16) =614a(17) =968a(18) =762a(19) =992a(20) =1482a(21) =1064a(22) =1106a(23) =1664a(24) =1562a(25) =1464a(26) =2186a(27) =1824a(28) =1742a(29) =3224