Math Help - Proving Cardinality

1. Proving Cardinality

Hello,
Urgently need some help with some Mathematical Communication.
The question is:
Show that the set of all odd square numbers {1,9,25,49,...} has cardinality ℵ0 [aleph-zero].

Any ideas?

2. Originally Posted by Ellis
Show that the set of all odd square numbers {1,9,25,49,...} has cardinality ℵ0 [aleph-zero].
The $k$-th non-negative odd number is $2k-1$...

Can you use this to find a bijection which maps $\mathbb{N}$ onto $\{1,9,25,49\ldots\}$ ?

3. Cardinality of R

What is the largest cardinality, because surely I can start with the cardinality of the set of all Real numbers and then work from there?

4. Originally Posted by Ellis
What is the largest cardinality
I don't know.
because surely I can start with the cardinality of the set of all Real numbers and then work from there?
I don't think so.