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 A170881 #15 Apr 15 2025 15:52:16
%S A170881 0,1,3,8,21,53,129,305,705,1601,3585,7937,17409,37889,81921,176129,
%T A170881 376833,802817,1703937,3604481,7602177,15990785,33554433,70254593,
%U A170881 146800641,306184193,637534209,1325400065,2751463425,5704253441,11811160065,24427626497,50465865729
%N A170881 a(0)=0; thereafter a(n) = (3*n+1)*2^(n-2)+1.
%H A170881 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (5,-8,4).
%F A170881 From _Chai Wah Wu_, Apr 15 2025: (Start)
%F A170881 a(n) = 5*a(n-1) - 8*a(n-2) + 4*a(n-3) for n > 4.
%F A170881 G.f.: x*(-x^3 - x^2 + 2*x - 1)/((x - 1)*(2*x - 1)^2). (End)
%F A170881 E.g.f.: (4*exp(x) - 3 + exp(2*x)*(3*x - 1))/4. - _Stefano Spezia_, Apr 15 2025
%t A170881 Join[{0,1},Table[(3n+1)2^(n-2)+1,{n,40}]] (* _Harvey P. Dale_, Nov 26 2023 *)
%Y A170881 Essentially the first column of the triangular array in A151747.
%Y A170881 Partial sums of A098156.
%K A170881 nonn,easy
%O A170881 0,3
%A A170881 _N. J. A. Sloane_, Jan 07 2010
%E A170881 Zero prepended by _Harvey P. Dale_, Nov 26 2023