Smallest k such that circle x^2 + y^2 = k passes through exactly 4n integer points.

Terms

a(0) =1a(1) =5a(2) =25a(3) =65a(4) =625a(5) =325a(6) =15625a(7) =1105a(8) =4225a(9) =8125a(10) =9765625a(11) =5525a(12) =244140625a(13) =203125a(14) =105625a(15) =27625a(16) =152587890625a(17) =71825a(19) =138125a(20) =2640625a(21) =126953125a(23) =160225a(24) =17850625a(25) =3173828125a(26) =1221025a(27) =3453125