3. A non-empty finite set of numbers is called a trivial set if the sum of the squares of all its elements is odd.

Let the set $A=\{1,2, \cdots, 2017\}$. Then the number of trivial sets among all proper subsets of $A$ is $\qquad$ (powers of numbers are allowed in the answer).
3. $2^{2016}-1$.

For the set $\{2,3, \cdots, 2017\}$, there are $2^{2016}-1$ non-empty proper subsets. Let there be $m$ trivial subsets and $2^{2016}-1-m$ other subsets. Then the trivial subsets in all proper subsets of set $A$ include:
(1) The trivial subsets of the proper subsets of $\{2,3, \cdots, 2017\}$, a total of $m$;
(2) $\{1\} \cup M$, where $M$ is a non-trivial subset of the proper subsets of $\{2,3, \cdots, 2017\}$, a total of $2^{2016}-1-m$.

Adding these gives the number of trivial subsets in all proper subsets of set $A$ as $2^{2016}-1$.