Question: Show that 155 can be expressed as the sum of a power of 2 and a cube number.
155 =
1. **State the problem:** We want to express $155$ as the sum of a power of $2$ and a cube number.
2. **Recall definitions:**
- A power of $2$ is any number of the form $2^n$ where $n$ is a non-negative integer.
- A cube number is any number of the form $m^3$ where $m$ is an integer.
3. **Approach:** We look for integers $n$ and $m$ such that:
$$155 = 2^n + m^3$$
4. **Try possible cube numbers less than $155$:**
- $1^3 = 1$
- $2^3 = 8$
- $3^3 = 27$
- $4^3 = 64$
- $5^3 = 125$
- $6^3 = 216$ (too large)
5. **Check each cube and see if $155 - m^3$ is a power of 2:**
- For $m=5$, $155 - 125 = 30$, which is not a power of 2.
- For $m=4$, $155 - 64 = 91$, not a power of 2.
- For $m=3$, $155 - 27 = 128$, which is $2^7$.
6. **Conclusion:**
$$155 = 2^7 + 3^3$$
This shows $155$ can be expressed as the sum of a power of 2 and a cube number.
**Final answer:**
$$155 = 128 + 27 = 2^7 + 3^3$$