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+Consider the digit d=1. After we write down each number n, we will update the number of ones that have occurred and call this number f(n,1). The first values for f(n,1), then, are as follows:
+So the first two solutions of the equation f(n,1)=n are n=0 and n=1. The next solution is n=199981.
+In the same manner the function f(n,d) gives the total number of digits d that have been written down after the number n has been written.