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 A138380 #18 Mar 08 2023 12:09:30
%S A138380 1,2,-1,-2,-4,-8,4,8,16,32,-16,-32,-64,-128,64,128,256,512,-256,-512,
%T A138380 -1024,-2048,1024,2048,4096,8192,-4096,-8192,-16384,-32768,16384,
%U A138380 32768,65536,131072,-65536,-131072,-262144,-524288,262144,524288,1048576,2097152
%N A138380 First differences of A138377.
%C A138380 All terms are powers of 2 (see comment in A138377). - _Michel Marcus_, Dec 01 2015
%H A138380 Colin Barker, <a href="/A138380/b138380.txt">Table of n, a(n) for n = 0..1000</a>
%H A138380 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,-4).
%F A138380 From _Colin Barker_, Dec 01 2015: (Start)
%F A138380 a(n) = -4*a(n-4) for n>3.
%F A138380 G.f.: (1-x)*(1+x)*(1+2*x) / ((1-2*x+2*x^2)*(1+2*x+2*x^2)).
%F A138380 (End)
%t A138380 Differences[LinearRecurrence[{0,0,0,-4},{0,1,3,2},60]] (* _Harvey P. Dale_, Mar 19 2012 *)
%t A138380 LinearRecurrence[{0, 0, 0, -4},{1, 2, -1, -2},59] (* _Ray Chandler_, Aug 03 2015 *)
%o A138380 (PARI) Vec((1-x)*(1+x)*(1+2*x)/((1-2*x+2*x^2)*(1+2*x+2*x^2)) + O(x^100)) \\ _Colin Barker_, Dec 01 2015
%Y A138380 Cf. A138377.
%K A138380 sign,easy
%O A138380 0,2
%A A138380 _Paul Curtz_, May 08 2008
%E A138380 More terms from _Harvey P. Dale_, Mar 19 2012
%E A138380 Missing terms added by _Colin Barker_, Dec 01 2015