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 A346386 #24 Aug 08 2021 01:42:22
%S A346386 1,10,36,45,136,325,666,820,1225,2080,3321,5050,7381,10440,11026,
%T A346386 14365,18721,19306,25425,32896,41905,52650,65341,80200,90100,97461,
%U A346386 101025,117370,140185,166176,195625,197506,228826,266085,307720,314821,354061,405450,454581,462241
%N A346386 Triangular numbers that are sum of squares of two distinct triangular numbers.
%e A346386 136, 10 and 6 are triangular numbers and 136 = 10^2 + 6^2 so 136 is a term.
%e A346386 820, 28 and 6 are triangular numbers and 820 = 28^2 + 6^2 so 820 is a term.
%t A346386 m = 50; t = Accumulate[Range[0, m]]; Select[Union[Plus @@@ Subsets[t^2, {2}]], # <= t[[-1]]^2 && IntegerQ @ Sqrt[8*# + 1] &] (* _Amiram Eldar_, Jul 16 2021 *)
%Y A346386 Cf. A000217, A004431, A037270, A073613.
%K A346386 nonn
%O A346386 1,2
%A A346386 _Metin Sariyar_, Jul 14 2021