"no idea how" or "no idea of how"

Could you tell me which sentence is correct regarding how to use "no idea how" and "no idea of how"

#1 I have no idea how to do it.

#2 I have no idea of how to do it.

At first, I didn't think #1 is ok.
But I googled(UK) "idea how ", it hits as many as about 23 times "idea of how". Which means, #1 is correct??
I think gramatically, #2 is also correct.

In conclusiton, are both correct?

Thank you!