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%I #13 Apr 22 2024 13:34:39
%S 0,30,2970,291060,28520940,2794761090,273858065910,26835295698120,
%T 2629585120349880,257672506498590150,25249276051741484850,
%U 2474171380564166925180,242443546019236617182820,23756993338504624316991210,2327942903627433946447955790,228114647562150022127582676240
%N Twice A200994.
%C Also 3 times A200993 and 6 times A352181.
%C Numbers that both doubles and triples of triangular numbers.
%H Editors, L'Intermédiaire des Mathématiciens, <a href="/A072256/a072256.pdf">Query 4500: The equation x(x+1)/2 = y*(y+1)/3</a>, L'Intermédiaire des Mathématiciens, 22 (1915), 255-260 (I).
%H Editors, L'Intermédiaire des Mathématiciens, <a href="/A072256/a072256_1.pdf">Query 4500: The equation x(x+1)/2 = y*(y+1)/3</a>, L'Intermédiaire des Mathématiciens, 22 (1915), 255-260 (II).
%H Editors, L'Intermédiaire des Mathématiciens, <a href="/A072256/a072256_2.pdf">Query 4500: The equation x(x+1)/2 = y*(y+1)/3</a>, L'Intermédiaire des Mathématiciens, 22 (1915), 255-260 (III).
%H Editors, L'Intermédiaire des Mathématiciens, <a href="/A072256/a072256_3.pdf">Query 4500: The equation x(x+1)/2 = y*(y+1)/3</a>, L'Intermédiaire des Mathématiciens, 22 (1915), 255-260 (IV).
%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (99,-99,1).
%F From _Chai Wah Wu_, Apr 22 2024: (Start)
%F a(n) = 99*a(n-1) - 99*a(n-2) + a(n-3) for n > 2.
%F G.f.: -30*x/((x - 1)*(x^2 - 98*x + 1)). (End)
%F a(n) = 30*A278620. - _Hugo Pfoertner_, Apr 22 2024
%Y Cf. A200993, A200994, A278620, A352181.
%K nonn,easy
%O 0,2
%A _N. J. A. Sloane_, Mar 08 2022
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