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 A363092 #11 May 19 2023 14:18:50
%S A363092 1,1,-4,-24,-64,-64,256,1536,4096,4096,-16384,-98304,-262144,-262144,
%T A363092 1048576,6291456,16777216,16777216,-67108864,-402653184,-1073741824,
%U A363092 -1073741824,4294967296,25769803776,68719476736,68719476736,-274877906944,-1649267441664,-4398046511104
%N A363092 a(n) = 4*a(n-1) - 8*a(n-2) with a(0) = a(1) = 1.
%D A363092 Paul J. Nahin, An Imaginary Tale: The Story of sqrt(-1), Princeton University Press, Princeton, NJ. 1998, pp. 94-96.
%H A363092 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (4,-8).
%F A363092 a(n) = 2^(3*n/2-1)*(2*cos(n*Pi/4) - sin(n*Pi/4)).
%F A363092 O.g.f.: (1 - 3*x)/(1 - 4*x + 8*x^2).
%F A363092 E.g.f.: exp(2*x)*(2*cos(2*x) - sin(2*x))/2.
%F A363092 a(n+1) = a(n) iff n is a multiple of 4.
%t A363092 LinearRecurrence[{4,-8},{1,1},29]
%Y A363092 Cf. A000045, A008586, A088137, A088138.
%K A363092 sign,easy
%O A363092 0,3
%A A363092 _Stefano Spezia_, May 19 2023