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 A380875 #13 Apr 02 2025 10:21:59
%S A380875 8,15,20,23,24,27,32,35,39,44,47,48,51,55,56,59,60,63,64,68,71,72,75,
%T A380875 76,79,80,84,87,91,92,95,96,99,104,111,112,115,116,119,120,123,124,
%U A380875 128,132,135,139,140,143,144,147,152,155,159,160,164,167,168,171,175,176,179,180,183,184,187,188
%N A380875 Indices of triangular numbers (A000217) which are also perimeters of integer-sided right triangles (A010814).
%C A380875 This is relevant for considering integer-sided right triangles whose sides are made of sticks of length 1, 2, 3, ..., n, using all those.
%C A380875 Sequence A382268 considers the special case where these sticks must be used in order.
%H A380875 Daniel Mondot, <a href="/A380875/b380875.txt">Table of n, a(n) for n = 1..10000</a>
%o A380875 (PARI) select( {is_A380875(n)=is_A010814(n*(n+1)\2)}, [1..222])
%Y A380875 Cf. A000217 (triangular numbers), A010814 (perimeters of right triangles), A382268 (subsequence of k for which a right triangle can be made with linked rods of length 1, ..., k).
%K A380875 nonn
%O A380875 1,1
%A A380875 _M. F. Hasler_, Mar 20 2025