If you multiply me by 2, subtract 1, and read the reverse the result you'll find me. Which numbers can I be?

Oft I must strive with wind and wave, Battle them both when under the sea
I feel out the bottom, a foreign land. In lying still I am strong in the strife;
If I fail in that they are stronger than I, And wrenching me loose, soon put me to rout.
They wish to capture what I must keep. I can master them both if my grip holds out,
If the rocks bring succor and lend support, Strength in the struggle. Ask me my name!

I'm in a zoo
But not in a jungle
I rarely come in pairs
But I'm in every puzzle


Some think I'm in a xylophone
But, I most certainly am not
You don't see me with a loan
But very strangely in a zealot


I'm in the magical prison of Azkaban
Well, can't you see?
I'm in the buzz of a fan
But, my oh my what could I be?