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 A274686 #23 Nov 19 2024 00:43:21 %S A274686 4,40,25,145,625,169,31249,985,2600,2500,87890625,3649,384199200, %T A274686 15625,33124,6409 %N A274686 Least number k such that k-th triangular number is the sum of two nonzero squares in exactly n ways. %C A274686 From _Robert Israel_, Jul 04 2016: (Start) %C A274686 Least k such that A025426(A000217(k)) = n. %C A274686 A025426(A000217(18463134765625))=17, but I don't know if this is minimal. (End) %C A274686 a(18) = 24649, a(20) = 40000, a(21) = 250000. 25*10^6, 25*10^8, 25*10^12 are not terms. Are there other terms of the form 25*10^(2k)? - _Chai Wah Wu_, Jul 23 2020 %e A274686 a(2) = 40 because 40*41 / 2 = 820 = 6^2 + 28^2 = 12^2 + 26^2. %Y A274686 Cf. A000217, A000404, A006339, A016032, A025426, A273238. %K A274686 nonn,more %O A274686 1,1 %A A274686 _Altug Alkan_, Jul 02 2016 %E A274686 a(11)-a(16) from _Giovanni Resta_, Jul 04 2016