A 7-digit telephone number d1 d2 d3 d4 d5 d6 d7 is called

A 7-digit telephone number d1 d2 d3 d4 d5 d6 d7 is called memorable if the prefix sequence, d1 d2 d3 is exactly the same as either of the sequences d4 d5 d6 or d5 d6 d7 (possibly both). Asume that each d1 can be any of the ten decimal digits 0, 1, 2, 3, ..., 9. What is the number of distinct memorable telephone numbers?