Only 19 givens, but there is no strong correlation between the difficulty and the number of givens. Note that no 4 is given, and only one 5.
First we spot that a 3 can be filled in:
and another 3:
and a third 3:
and a fourth 3:
Let us mark some pairs for possible future use.
So far for the 3's. There is also a 6 in the upper left hand corner:
and another one in the lower left hand corner:
and another one:
Adding a few pairs:
.. (continued) ..