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%I #19 Apr 25 2024 09:19:24
%S 0,4,35,279,2200,17324,136395,1073839,8454320,66560724,524031475,
%T 4125691079,32481497160,255726286204,2013328792475,15850904053599,
%U 124793903636320,982500325036964,7735208696659395,60899169248238199
%N Numbers k such that (3*(2*k + 1)^2 + 2)/5 is a square.
%C Square roots of (3*(2*k+1)^2+2)/5 are listed in A070997, therefore (3*(2*a(n) + 1)^2 + 2)/5 = A070997(n-1)^2.
%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (9,-9,1).
%F a(n+2) = 8*a(n+1) - a(n) + 3.
%F From _R. J. Mathar_, Oct 24 2008: (Start)
%F G.f.: x^2*(4 - x)/((1 - x)*(1 - 8*x + x^2)).
%F a(n) = (A057080(n-1)-1)/2. (End)
%Y Cf. A070997, A131751.
%Y Cf. A001091 (first differences).
%K nonn,easy,changed
%O 1,2
%A _Richard Choulet_, Oct 14 2008
%E a(4) corrected, extended, definition corrected by _R. J. Mathar_, Oct 24 2008
%E Offset changed by _Bruno Berselli_, Apr 06 2018
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