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 A290505 #15 Dec 31 2019 00:02:05
%S A290505 203125,265625,406250,453125,531250,578125,609375,640625,796875,
%T A290505 812500,828125,906250,953125,1062500,1140625,1156250,1218750,1281250,
%U A290505 1359375,1390625,1421875,1515625,1578125,1593750,1625000,1656250,1703125,1734375,1765625,1812500
%N A290505 Hypotenuses for which there exist exactly 19 distinct integer triangles.
%C A290505 Numbers whose square is decomposable in 19 different ways into the sum of two nonzero squares: these are those with exactly two distinct prime divisors of the form 4k+1 with one, and six respective multiplicities, or with only one prime divisor of this form with multiplicity nineteen.
%H A290505 Ray Chandler, <a href="/A290505/b290505.txt">Table of n, a(n) for n = 1..10000</a> (first 1000 terms from Hamdi Sahloul)
%F A290505 Terms are obtained by the products A004144(k)*A002144(p1)*A002144(p2)^6, or A004144(k)*A002144(p1)^19 for k, p1, p2 > 0 ordered by increasing values.
%e A290505 a(1) = 203125 = 5^6*13, a(5) = 531250 = 2*5^6*17, a(281) = 12796875 = 3^2*5^6*7*13.
%t A290505 r[a_]:={b, c}/.{ToRules[Reduce[0<b<c && a^2 == b^2 + c^2, {b, c}, Integers]]}; Select[Range[12796875], Length[r[#]] == 19 &] (* _Vincenzo Librandi_, Mar 01 2016 *)
%Y A290505 Cf. A002144, A006339, A046080, A046109, A083025.
%Y A290505 Cf. A004144 (0), A084645 (1), A084646 (2), A084647 (3), A084648 (4), A084649 (5), A097219 (6), A097101 (7), A290499 (8), A290500 (9), A097225 (10), A290501 (11), A097226 (12), A097102 (13), A290502 (14), A290503 (15), A097238 (16), A097239 (17), A290504 (18), A097103 (22), A097244 (31), A097245 (37), A097282 (40), A097626 (67).
%K A290505 nonn
%O A290505 1,1
%A A290505 _Hamdi Sahloul_, Aug 04 2017