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 A155559 #30 Aug 26 2025 14:25:32
%S A155559 0,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192,16384,32768,65536,
%T A155559 131072,262144,524288,1048576,2097152,4194304,8388608,16777216,
%U A155559 33554432,67108864,134217728,268435456,536870912,1073741824,2147483648,4294967296,8589934592
%N A155559 a(n) = 2*A131577(n).
%C A155559 Essentially the same as A131577, A046055, A011782, A000079 and A034008.
%H A155559 <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (2).
%F A155559 a(n) = A000079(n), n>0.
%F A155559 a(n) = (-1)^(n+1)*A084633(n+1).
%F A155559 a(n) + A155543(n) = 2^n+4^n = A063376(n) = 2*A007582(n) =2*A137173(2n+1).
%F A155559 Conjecture: a(n) = A090129(n+3)-A090129(n+2).
%F A155559 G.f.: 2*x/(1-2*x). - _R. J. Mathar_, Jul 23 2009
%F A155559 E.g.f.: exp(2*x) - 1. - _Stefano Spezia_, Aug 26 2025
%t A155559 CoefficientList[ Series[ 2x/(1 - 2x), {x, 0, 32}], x] (* _Robert G. Wilson v_, Aug 08 2018 *)
%o A155559 (PARI) a(n)=if(n,2^n,0) \\ _Charles R Greathouse IV_, Aug 01 2016
%o A155559 (Python)
%o A155559 def A155559(n): return 1<<n if n else 0 # _Chai Wah Wu_, Sep 05 2024
%Y A155559 Cf. A000079, A007582, A011782, A034008, A046055, A063376, A084633, A090129, A131577, A137173.
%K A155559 nonn,easy,changed
%O A155559 0,2
%A A155559 _Paul Curtz_, Jan 24 2009
%E A155559 Edited by _R. J. Mathar_, Jul 23 2009
%E A155559 Extended by _Omar E. Pol_, Nov 19 2012