Problem Archive

For a positive integer $k$, define $d(k)$ as the sum of the digits of $k$ in its usual decimal representation. Thus $d(42) = 4+2 = 6$.

For a positive integer $n$, define $S(n)$ as the number of positive integers $k \lt 10^n$ with the following properties :

• $k$ is divisible by $23$ and
• $d(k) = 23$.

You are given that $S(9) = 263626$ and $S(42) = 6377168878570056$.

Find $S(11^{12})$ and give your answer mod $10^9$.