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%I #30 Dec 31 2023 16:08:00
%S 4,9,4,9,4,9,4,9,4,9,4,9,4,9,4,9,4,9,4,9,4,9,4,9,4,9,4,9,4,9,4,9,4,9,
%T 4,9,4,9,4,9,4,9,4,9,4,9,4,9,4,9,4,9,4,9,4,9,4,9,4,9,4,9,4,9,4,9,4,9,
%U 4,9,4,9,4,9,4,9,4,9,4,9,4
%N Period 2: repeat [4, 9].
%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (0,1).
%F G.f.: (4+9x)/((1-x)*(1+x)). - _R. J. Mathar_, Nov 21 2011
%F From _Wesley Ivan Hurt_, Dec 31 2023: (Start)
%F a(n) = a(n-2) for n>1 with a(0)=4, a(1)=9.
%F a(n) = (13-5*(-1)^n)/2. (End)
%t Table[4 + 5 Mod[n, 2], {n, 0, 50}] (* _Jinyuan Wang_, Feb 26 2020 *)
%o (PARI) a(n)=4+n%2*5 \\ _Charles R Greathouse IV_, Dec 21 2011
%Y Cf. A176219.
%K nonn,easy
%O 0,1
%A _N. J. A. Sloane_
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