This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A216408 #15 Sep 19 2012 18:13:23 %S A216408 1,2209,27889,96721,146689,229441,253009,418609,516961,703921,786769, %T A216408 966289,1324801,1495729,1739761,2211169,2283121,2430481,3323329, %U A216408 3411409,4255969,4879681,5527201,5755201,7091569,7219969,8427409,8994001,9138529,10029889,10182481,11282881,11607649,12439729,13476241,14922769,15295921 %N A216408 Perfect squares which can be written neither as a^2+b^2, nor as a^2+2*b^2, nor as a^2+3*b^2, nor as a^2+7*b^2, with a > 0 and b > 0. %C A216408 If a composite number C, in case, can be written in the form C = a^2+k*b^2, for some integers a & b, then every prime factor P (for C) being raised to an odd power can be written in the form P = c^2+k*d^2, for some integers c & d. %C A216408 This statement is only true for k = 1, 2, 3. %C A216408 For k = 7, with the exception of the prime factor 2, the statement mentioned above is true. %Y A216408 Cf. A216451, A216500, A216501, A216671, A216679, A216680, A216682 %K A216408 nonn %O A216408 1,2 %A A216408 _V. Raman_, Sep 17 2012