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 A328499 #18 Nov 13 2019 10:50:51
%S A328499 0,0,0,0,0,0,0,0,0,0,0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2,2,2,2,2,
%T A328499 2,2,2,2,2,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,4,4,4,4,4,4,4,4,4,4,4,4,4,
%U A328499 4,5,5,5,5,5,5,5,5,5,5,5,5,5,5,6,6,6,6,6,6,7,7,7,7,7,7,7,7,7,7,7
%N A328499 The number of primitive Pythagorean triangles with perimeter less than n.
%C A328499 D. N. Lehmer has proved that the asymptotic density of a(n) is a(n)/n = log(2)/Pi^2 = 0.07023049... See A118858.
%H A328499 Ron Knott, <a href="http://www.maths.surrey.ac.uk/hosted-sites/R.Knott/Pythag/pythag.html">Pythagorean Triples and Online Calculators</a>
%H A328499 D. N. Lehmer, <a href="http://www.jstor.org/stable/2369728">Asymptotic evaluation of certain totient sums</a>, Amer. J. Math. 22, 293-335, 1900.
%e A328499 For n=90, the triples are
%e A328499 {3, 4, 5}, 3 + 4 + 5 = 12 < 90
%e A328499 {5, 12, 13}, 5 + 12 + 13 = 30 < 90
%e A328499 {7, 24, 25}, 7 + 24 + 25 = 56 < 90
%e A328499 {8, 15, 17}, 8 + 15 + 17 = 40 < 90
%e A328499 {9, 40, 41}, 9 + 40 + 41 = 90
%e A328499 {12, 35, 37}, 12 + 35 + 37 = 84 < 90
%e A328499 {20, 21, 29}, 20 + 21 + 29 = 70 < 90
%e A328499 so a(90)=7.
%Y A328499 Cf. A008846, A024364, A118858, A249750.
%K A328499 nonn,easy
%O A328499 1,30
%A A328499 _Mo Li_, Oct 17 2019