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A379609 Triples (x,y,z) such that T(x)*T(y) = T(z) with 2 <= x <= y, where T(n) is the n-th triangular number, sorted first by values of z, then by values of x.

%I A379609 #32 Jan 17 2025 19:37:07
%S A379609 3,3,8,2,5,9,4,6,20,2,20,35,3,14,35,4,12,39,5,11,44,7,10,55,5,19,75,3,
%T A379609 34,84,9,13,90,6,21,98,2,76,132,6,33,153,4,55,175,14,18,189,13,20,195,
%U A379609 12,23,207,15,20,224,14,22,230,11,28,231,12,29,260,7,51,272,10,38,285,11,36,296,5,90,350,3,143,351,10,50,374,7,75,399,9,68,459,19,34,475
%N A379609 Triples (x,y,z) such that T(x)*T(y) = T(z) with 2 <= x <= y, where T(n) is the n-th triangular number, sorted first by values of z, then by values of x.
%e A379609 Triples begin:
%e A379609   3,  3,  8;
%e A379609   2,  5,  9;
%e A379609   4,  6, 20;
%e A379609   2, 20, 35;
%e A379609   3, 14, 35;
%e A379609   4, 12, 39;
%e A379609   5, 11, 44;
%e A379609   7, 10, 55;
%e A379609   ...
%e A379609 The triple 2,5,9 is in this sequence because the second triangular number (3) times the fifth (15) is the ninth (45).
%Y A379609 Cf. A000217, A188630, A198453 (additive), A225390.
%K A379609 nonn,tabf
%O A379609 1,1
%A A379609 _Kelvin Voskuijl_, Dec 27 2024