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 A089907 #22 Mar 26 2024 14:46:00
%S A089907 0,21,483,7785,107787,1377789,16777791,197777793,2277777795,
%T A089907 25777777797,287777777799,3177777777801,34777777777803,
%U A089907 377777777777805,4077777777777807,43777777777777809,467777777777777811
%N A089907 Sum of digits of numbers between 0 and (6/9)*(10^n-1).
%C A089907 From a suggestion of _Yalcin Aktar_
%H A089907 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (22,-141,220,-100).
%F A089907 a(n) = s(6, n-1) where s(a, k)=a*(k+1)+a^2*sum(i=0, k, i*10^(k-i))+sum(i=0, k, 5*a*(9*(k-i)+a- 1)*10^(k-i-1)).
%F A089907 a(n) = (-11/9*(-1+10^n)+(2+3*10^n)*n). G.f.: 3*x*(40*x^2+7*x+7) / ((x-1)^2*(10*x-1)^2). - _Colin Barker_, Jun 14 2013
%t A089907 LinearRecurrence[{22,-141,220,-100},{0,21,483,7785},20] (* _Harvey P. Dale_, Aug 22 2022 *)
%Y A089907 Cf. A089903, A089904, A089905, A087330, A089906, A089908, A089909, A034967.
%K A089907 nonn,base,easy
%O A089907 0,2
%A A089907 _Benoit Cloitre_, Nov 14 2003