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 A186942 #9 Feb 22 2023 17:04:38
%S A186942 1,3,15,79,383,1727,7423,30975,126975,515071,2076671,8343551,33456127,
%T A186942 134004735,536412159,2146500607,8587837439,34355281919,137429516287,
%U A186942 549735890943,2198981312511,8796004941823,35184187539455,140737102479359,562949148114943,2251798135963647
%N A186942 a(n)=2(4^n-n*2^n)-1.
%C A186942 A factor in the Hankel transform A186941.
%H A186942 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (9,-28,36,-16).
%F A186942 G.f.: (1-6x+16x^2-8x^3)/((1-2x)^2*(1-5x+4x^2)).
%t A186942 Table[2(4^n-n 2^n)-1,{n,0,30}] (* or *) LinearRecurrence[{9,-28,36,-16},{1,3,15,79},30] (* _Harvey P. Dale_, Feb 22 2023 *)
%K A186942 nonn,easy
%O A186942 0,2
%A A186942 _Paul Barry_, Mar 01 2011