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 A087456 #11 Sep 06 2018 19:23:15
%S A087456 5,101,181,313,353,373,505,545,565,757,797,929,949,10001,10201,10301,
%T A087456 10501,10601,12421,12721,12821,14341,14741,16061,16361,16561,16661,
%U A087456 16861,18181,18281,18481,18581,31013,31313,31513,31613,31813,33133
%N A087456 Palindromic hypotenuses in primitive Pythagorean triples.
%C A087456 For prime terms in this sequence, see A081220. - _Lekraj Beedassy_, Jun 30 2008
%t A087456 Take[Select[Sqrt[#[[1]]^2+#[[2]]^2]&/@(Union[Sort/@({Times@@#,(Last[#]^2- First[#]^2)/2}&/@(Select[Subsets[Range[1,311,2],{2}],GCD@@#== 1&]))]), PalindromeQ]//Union,50] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Sep 06 2018 *)
%Y A087456 Cf. A020882.
%K A087456 nonn,base
%O A087456 1,1
%A A087456 _Lekraj Beedassy_, Oct 23 2003
%E A087456 More terms from _Ray Chandler_, Oct 25 2003