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%I #23 Oct 11 2020 05:55:21
%S 5,7,9,13,19,29,45,71,113,181,291,469,757,1223,1977,3197,5171,8365,
%T 13533,21895,35425,57317,92739,150053,242789,392839,635625,1028461,
%U 1664083,2692541,4356621,7049159,11405777,18454933,29860707,48315637
%N Perimeter of integer triangle (A001611(n), A001611(n+1), A001611(n+2)).
%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (2,0,-1).
%F a(n) = 2*A001611(n+2) + 1;
%F a(n) = a(n-1) + 2*A000045(n).
%F a(n) = A001611(n) + A001611(n+1) + A001611(n+2).
%F a(n) = 2*a(n-1) - a(n-3).
%F G.f.: -(5*x^2 + 3*x - 5) / ((x-1)*(x^2 + x - 1)). - _Colin Barker_, Apr 10 2013
%F a(n) = 2*Fibonacci(n+2) + 3. - _Greg Dresden_, Oct 10 2020
%t Fibonacci[Range[2, 5! ]]*2+3 (* _Vladimir Joseph Stephan Orlovsky_, Mar 19 2010 *)
%t LinearRecurrence[{2,0,-1},{5,7,9},40] (* _Harvey P. Dale_, Nov 12 2015 *)
%Y Cf. A000045, A001611, A097281.
%K nonn,easy
%O 0,1
%A _Reinhard Zumkeller_, Aug 04 2004
%E Corrected by _T. D. Noe_, Oct 25 2006