A radioactive nucleus A undergoes a series of decays according to following scheme
`A overset(alpha)to A_1 overset(-beta)to A_2 overset(alpha)toA_3 overset(gamma)toA_4`
The mass number and atomic number of A4 are 172 and 69 respectively. What are these numbers for A ?

Explanation

To solve the problem, we need to analyze the decay process of the radioactive nucleus A step by step. We will track the changes in mass number (A) and atomic number (Z) through each decay event.

### Step-by-Step Solution:

1. **Identify the final nucleus (A4)**:
- We are given that the mass number (A) of nucleus A4 is 172 and the atomic number (Z) is 69.

2. **Understand the decay process**:
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