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 A171449 #13 Aug 27 2025 09:11:46
%S A171449 -1,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192,16384,32768,65536,
%T A171449 131072,262144,524288,1048576,2097152,4194304,8388608,16777216,
%U A171449 33554432,67108864,134217728,268435456,536870912,1073741824,2147483648,4294967296,8589934592
%N A171449 Powers of 2 (A000079) with 1 changed to -1.
%H A171449 <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (2).
%F A171449 From _Stefano Spezia_, Aug 26 2025: (Start)
%F A171449 G.f.: -(1 - 4*x)/(1 - 2*x).
%F A171449 E.g.f.: exp(2*x) - 2. (End)
%t A171449 Join[{-1}, 2^Range[50]] (* _Paolo Xausa_, Aug 27 2025 *)
%Y A171449 Cf. A000079.
%K A171449 sign,easy,changed
%O A171449 0,2
%A A171449 _Paul Curtz_, Dec 09 2009
%E A171449 Edited by _N. J. A. Sloane_, Dec 17 2009