Question 24
Call a $7$-digit telephone number $d_1d_2d_3$-$d_4d_5d_6d_7$ *memorable* if the prefix sequence $d_1d_2d_3$ is exactly the same as either of the sequences $d_4d_5d_6$ or $d_5d_6d_7$ (possibly both). Assuming that each $d_i$ can be any of the ten decimal digits $0,$ $1,$ $2,$ $\ldots,$ $9,$ the number of different memorable telephone numbers is