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 A141023 #34 Sep 08 2022 08:45:35
%S A141023 0,0,3,6,15,30,63,126,255,510,1023,2046,4095,8190,16383,32766,65535,
%T A141023 131070,262143,524286,1048575,2097150,4194303,8388606,16777215,
%U A141023 33554430,67108863,134217726,268435455,536870910,1073741823,2147483646,4294967295,8589934590,17179869183
%N A141023 a(n) = 2^n - (3-(-1)^n)/2.
%H A141023 Vincenzo Librandi, <a href="/A141023/b141023.txt">Table of n, a(n) for n = 0..1000</a>
%H A141023 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (2,1,-2).
%F A141023 a(n) = A000079(n) - A000034(n).
%F A141023 a(n) = 3*A000975(n-1).
%F A141023 G.f.: 3*x^2/( (x-1)*(2*x-1)*(1+x) ). - _R. J. Mathar_, Jul 07 2011
%t A141023 Range[0,20]! CoefficientList[Series[D[(Cosh[x]-1)(Exp[x]-1), x], {x,0,20}], x] (* _Geoffrey Critzer_, Dec 03 2011 *)
%t A141023 LinearRecurrence[{2, 1, -2}, {0, 0, 3}, 60] (* _Vladimir Joseph Stephan Orlovsky_, Feb 14 2012 *)
%t A141023 Table[2^n - (3 - (-1)^n)/2, {n, 0, 34}] (* _Alonso del Arte_, Feb 14 2012 *)
%o A141023 (Magma) [2^n -(3-(-1)^n)/2: n in [0..40]]; // _Vincenzo Librandi_, Aug 08 2011
%o A141023 (PARI) x='x+O('x^50); concat([0,0], Vec(3*x^2/((x-1)*(2*x-1)*(1+x)))) \\ _G. C. Greubel_, Oct 10 2017
%Y A141023 Cf. A062510 (first differences).
%K A141023 nonn,easy
%O A141023 0,3
%A A141023 _Paul Curtz_, Jul 29 2008