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A089907
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Sum of digits of numbers between 0 and (6/9)*(10^n-1).
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6
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0, 21, 483, 7785, 107787, 1377789, 16777791, 197777793, 2277777795, 25777777797, 287777777799, 3177777777801, 34777777777803, 377777777777805, 4077777777777807, 43777777777777809, 467777777777777811
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OFFSET
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0,2
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COMMENTS
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LINKS
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FORMULA
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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)).
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
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MATHEMATICA
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LinearRecurrence[{22, -141, 220, -100}, {0, 21, 483, 7785}, 20] (* Harvey P. Dale, Aug 22 2022 *)
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CROSSREFS
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KEYWORD
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nonn,base,easy
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AUTHOR
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STATUS
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approved
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