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A089906
Sum of digits of numbers between 0 and (4/9)*(10^n-1).
6
0, 10, 270, 4650, 66430, 864210, 10641990, 126419770, 1464197550, 16641975330, 186419753110, 2064197530890, 22641975308670, 246419753086450, 2664197530864230, 28641975308642010, 306419753086419790
OFFSET
0,2
COMMENTS
From a suggestion of Yalcin Aktar
FORMULA
a(n) = s(4, 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) = (2*(-55*(-1+10^n)+9*(10+9*10^n)*n))/81. G.f.: 10*x*(12*x^2+5*x+1) / ((x-1)^2*(10*x-1)^2). - Colin Barker, Jun 14 2013
KEYWORD
nonn,base,easy
AUTHOR
Benoit Cloitre, Nov 14 2003
STATUS
approved