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%I #24 Nov 07 2019 14:00:55
%S 27,36,81,72,135,108,189,144,243,180,297,216,351,252,405,288,459,324,
%T 513,360,567,396,621,432,675,468,729,504,783,540,837,576,891,612,945,
%U 648,999,684,1053,720,1107
%N a(n) = A144433(3n+1) + A144433(3n+2) + A144433(3n+3).
%C All terms are multiples of 9.
%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0, 2, 0, -1).
%F From _R. J. Mathar_, May 21 2009: (Start)
%F G.f.: 9*(3+4*x+3*x^2)/((x-1)^2*(1+x)^2).
%F a(n) = 45*(n+1)/2 + 9*(-1)^n*(n+1)/2. (End)
%F a(n) = 9*A106833(n+1). - _Jean-François Alcover_, Feb 02 2019, after _Paul Curtz_
%F a(n+4) = 2*a(n+2) - a(n). - _Jianing Song_, Feb 04 2019
%t Table[(9/2)(5 + (-1)^n)(n + 1), {n, 0, 40}] (* _Jean-François Alcover_, Feb 02 2019 *)
%t LinearRecurrence[{0,2,0,-1},{27,36,81,72},50] (* _Harvey P. Dale_, Nov 07 2019 *)
%o (PARI) a(n) = 45*(n+1)/2 + 9*(-1)^n*(n+1)/2 \\ _Jianing Song_, Feb 04 2019
%Y Cf. A106933, A144433.
%K nonn,easy
%O 0,1
%A _Paul Curtz_, Nov 22 2008
%E Edited by _R. J. Mathar_, May 21 2009
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