help me, i can't find error in my algo.

for (n = 3, k = 10)
we have 1 case
x00, where x can take (k-1) digits
(anyway first digit can take k - 1)
so answer is 9*10^2 - 9 = 891  - right!

for (n = 4, k = 10)
we have 2 cases:
x00y  - y can take k digits - 9*10
xx00  - 9*9
answer  - 9*10^3 - 90 - 81 = 8829 - right

for(n = 5, k = 10)
we have 3 cases
x00yy (9*10^2)
xx00y (9^2*10)
xxx00 (9^3)
we have 87561, but right answer is 87480

Edited by author 23.12.2007 15:29

for(n = 5,k = 10)
You are wrong

Right answer
x00yy(9*10^2)
xx00y(9^2*10)
xyx00(9^2*10) //!!!xYx00
87480