MathNet 2026 — Part 06 Question 137

Find seven four digit positive integers $a_1, a_2, a_3, a_4, a_5, a_6, a_7$ which form a geometric progression i.e. $\frac{a_2}{a_1} = \frac{a_3}{a_2} = \frac{a_4}{a_3} = \frac{a_5}{a_4} = \frac{a_6}{a_5} = \frac{a_7}{a_6}$.