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 A383958 #18 Jul 13 2025 17:24:33
%S A383958 1,1,7,49,391,3527,34847,368081,4089799,47278087,564211231,6911587591,
%T A383958 86537984287,1103800819999,14305258627199,187980039148049,
%U A383958 2500329655657799,33615543148288199,456277455475379999,6246438365457952199,86175353776521952799,1197196443787879360799,16738118900293300099199
%N A383958 Sum of the legs of the unique primitive Pythagorean triple (a,b,c) such that (a-b+c)/2 = A000108(n) and its long leg and hypotenuse are consecutive natural numbers.
%H A383958 José Miguel Blanco Casado and Miguel-Ángel Pérez García-Ortega, <a href="/A383834/a383834.pdf">El Libro de las Ternas Pitagóricas</a>
%F A383958 a(n) = A383615(n,1) + A383615(n,2).
%F A383958 a(n) = 2*A000108(n)^2 - 1.
%F A383958 a(n) = 2*A001246(n) - 1.
%e A383958 For n=3, the short leg is A383615(3,1) = 3 and the long leg is A383615(3,2) = 4 so the sum of the legs is then a(3) = 3 + 4 = 7.
%t A383958 a=Table[(2n)!/(n!(n+1)!),{n,0,23}];Apply[Join,Map[{2#^2-1}&,a]]
%Y A383958 Cf. A000108, A383615, A131428, A383616, A381846, A001246.
%K A383958 nonn,easy
%O A383958 0,3
%A A383958 _Miguel-Ángel Pérez García-Ortega_, May 16 2025