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 A158561 #16 Mar 19 2024 10:25:21
%S A158561 3,7,26,100,392,1552,6176,24640,98432,393472,1573376,6292480,25167872,
%T A158561 100667392,402661376,1610629120,6442483712,25769869312,103079346176,
%U A158561 412317122560,1649267965952,6597070815232,26388281163776,105553120460800,422212473454592
%N A158561 a(n) = ((2^n)*((2^n)+1) - (2^(n-1))*((2^(n-1))+1))/2, a(1)=3.
%C A158561 a(n) gives the number of elements with the length of n-digits, base B, in the addition matrix <0;B^n -1> x <0;B^n -1>. a(1)=B*(B+1)/2. a(n)=((B^n)*((B^n)+1) - (B^(n-1))*((B^(n-1))+1))/2.
%C A158561 Essentially the same as A049775. [_R. J. Mathar_, Mar 26 2009]
%H A158561 Harvey P. Dale, <a href="/A158561/b158561.txt">Table of n, a(n) for n = 1..1000</a>
%H A158561 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (6,-8)
%F A158561 G.f.: x*(1-x)*(3-8*x)/((1-2*x)*(1-4*x)). [_Jaume Oliver Lafont_, Mar 27 2009]
%F A158561 G.f.: (3-11*x+8*x^2)/(1-6*x+8*x^2). - _Harvey P. Dale_, Feb 25 2017
%t A158561 LinearRecurrence[{6,-8},{3,7,26},30] (* _Harvey P. Dale_, Feb 25 2017 *)
%Y A158561 Cf. A000217
%Y A158561 Cf. A006516. [_Jaume Oliver Lafont_, Mar 27 2009]
%K A158561 easy,nonn
%O A158561 1,1
%A A158561 _Ctibor O. Zizka_, Mar 21 2009
%E A158561 More terms from _Harvey P. Dale_, Feb 25 2017