Deficiency of squares: a(n) = 2n^2 - sigma(n^2).

Terms

a(0) =1a(1) =1a(2) =5a(3) =1a(4) =19a(5) =-19a(6) =41a(7) =1a(8) =41a(9) =-17a(10) =109a(11) =-115a(12) =155a(13) =-7a(14) =47a(15) =1a(16) =271a(17) =-199a(18) =341a(19) =-161a(20) =141a(21) =37a(22) =505a(23) =-499a(24) =469a(25) =71a(26) =365a(27) =-199a(28) =811a(29) =-1021