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%I #23 Mar 26 2024 14:45:57
%S 0,28,609,9555,130501,1654947,20049393,235493839,2704938285,
%T 30549382731,340493827177,3754938271623,41049382716069,
%U 445493827160515,4804938271604961,51549382716049407,550493827160493853
%N Sum of digits of numbers between 0 and (7/9)*(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(7, 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) = (7*(-22*(-1+10^n)+9*(4+9*10^n)*n))/162. G.f.: 7*x*(15*x^2-x+4) / ((x-1)^2*(10*x-1)^2). - _Colin Barker_, Jun 14 2013
%Y Cf. A089903, A089904, A089905, A087330, A089906, A089907, A089909, A034967.
%K nonn,base,easy
%O 0,2
%A _Benoit Cloitre_, Nov 14 2003
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