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