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 A380825 #15 Feb 13 2025 12:20:58 %S A380825 8,9,20,24,27,35,39,44,54,55,75,80,84,90,98,99,104,132,135,153,175, %T A380825 189,195,207,224,230,231,252,260,272,275,279,285,296,324,350,351,374, %U A380825 399,405,440,455,459,475,494,539,560,567,575,594,615,620,624,665,675 %N A380825 Indices of triangular numbers that are the products of triangular numbers larger than 1. %F A380825 a(n) = A003056(A068143(n)). %F A380825 A000217(a(n)) = A068143(n). %e A380825 20 is a term as the 20th triangular number is 210 = 21*10 both triangular numbers. %e A380825 24 is also a term since the 24th triangular number is 300 = 3*10*10. %Y A380825 Cf. A000217, A003056, A068143. %K A380825 nonn %O A380825 1,1 %A A380825 _Kelvin Voskuijl_, Feb 04 2025