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 A216680 #10 Sep 16 2012 08:58:24 %S A216680 1,14,15,30,35,42,46,47,55,60,62,69,70,78,87,94,95,105,110,115,119, %T A216680 120,126,135,138,140,141,142,143,154,155,158,159,165,167,168,174,182, %U A216680 186,188,190,195,206,210,213,215,220,222,230,231,235,238,240,248,254,255,266,270,276,280,282,285,286,287,295,299 %N A216680 Numbers 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 A216680 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 A216680 This statement is only true for k = 1, 2, 3. %C A216680 For k = 7, with the exception of the prime factor 2, the statement mentioned above is true. %C A216680 Essentially the same as A216679. - _R. J. Mathar_, Sep 16 2012 %Y A216680 Cf. A216451, A216500. %K A216680 nonn %O A216680 1,2 %A A216680 _V. Raman_, Sep 13 2012