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%I #16 Mar 16 2024 04:33:43
%S 4,9,9,49,225,961,3969,16129,65025,261121,1046529,4190209,16769025,
%T 67092481,268402689,1073676289,4294836225,17179607041,68718952449,
%U 274876858369,1099509530625,4398042316801,17592177655809
%N Smallest square k == 1 (mod some n-th power), k > 1.
%C From a(2) onwards the n-th power that divides a(n) -1 is 2^n ===> Second term onwards same as A060867 i.e. a(n+1) = (2^n-1)^2.
%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (7,-14,8).
%F From _Colin Barker_, Feb 05 2013: (Start)
%F a(n) = (2^n-2)^2/4 for n>2.
%F a(n) = 7*a(n-1)-14*a(n-2)+8*a(n-3) for n>5.
%F G.f.: x*(2*x+1)*(32*x^3-56*x^2+27*x-4) / ((x-1)*(2*x-1)*(4*x-1)). (End)
%e a(6) = 961 and 960 = 64*15.
%Y Cf. A060867.
%K nonn,easy
%O 1,1
%A _Amarnath Murthy_, Sep 19 2003
%E More terms from _Ray Chandler_, Oct 04 2003
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