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 A255239 #4 Mar 12 2015 11:17:55 %S A255239 1,1,2,3,3,4,3,5,4,7,6,8,7,10,6,9,6,11,9,14,11,15,10,15,11,14,11,18, %T A255239 14,19,14,18,13,20,15,23,16,25,21,24,19,23,16,27,20,28,21,30,22,27,22, %U A255239 31,25,34,27,35,24,35,26,32,29,36,26,39,28 %N A255239 Alternating row sums of triangle A255238. %C A255239 See A255238 for a Gauss' circle problem comment and a link. %F A255239 a(n) = sum((-1)^m*T(n, m), m = 0..n), n >= 0, with T(n, m) = A255238(n, m) = 1 + floor(sqrt(n^2 - m^2)). %Y A255239 Cf. A255238. %K A255239 nonn,easy %O A255239 0,3 %A A255239 _Wolfdieter Lang_, Mar 12 2015