This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A087124 #28 Aug 17 2024 14:06:31
%S A087124 1,3,6,15,37,94,241,623,1618,4215,11001,28746,75169,196651,514606,
%T A087124 1346879,3525565,9229062,24160401,63250167,165586906,433505383,
%U A087124 1134920881,2971243730,7778788417,20365086099,53316412566,139584058863
%N A087124 a(n) = Fibonacci(n) + Fibonacci(2n+1).
%C A087124 Binomial transform of A087123.
%C A087124 For n>=1, a(n) is the coefficient of x in the reduction by x^2->x+1 of the polynomial 1+x^n+x^(2n+1). For an introduction to reductions of polynomials by substitutions such as x^2->x+1, see A192232. - _Clark Kimberling_, Jul 01 2011
%H A087124 Vincenzo Librandi, <a href="/A087124/b087124.txt">Table of n, a(n) for n = 0..1000</a>
%H A087124 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (4,-3,-2,1).
%F A087124 G.f.: (1-2*x)*(1+x-x^2)/((1-3*x+x^2)*(1-x-x^2)). - _Colin Barker_, Mar 12 2012
%t A087124 CoefficientList[Series[(1-2*x)*(1+x-x^2)/((1-3*x+x^2)*(1-x-x^2)),{x,0,1001}],x] (* _Vincenzo Librandi_, Mar 13 2012 *)
%t A087124 LinearRecurrence[{4,-3,-2,1},{1,3,6,15},30] (* _Harvey P. Dale_, Aug 17 2024 *)
%o A087124 (Magma) [Fibonacci(n)+Fibonacci(2*n+1): n in [0..40]]; // _Vincenzo Librandi_, Mar 13 2012
%o A087124 (PARI) a(n)=fibonacci(n)+fibonacci(2*n+1) \\ _Charles R Greathouse IV_, Mar 13 2012
%Y A087124 Cf. A000045, A087123, A192232.
%K A087124 easy,nonn
%O A087124 0,2
%A A087124 _Paul Barry_, Aug 15 2003