What is the chance of getting a back to back shiny?

Question

Remember the shiny zoroark I encountered. The next encounter was a shiny Audino.

Answer 1

In B2W2 specifically, each one had a 1/8192 chance, making for a chance of (1/8192)^2 or 1/67,108,864

Answer 2

I think the base odds are 1 on 512 so I think the odds of back to back are 512x512.

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This would be true if you started from scratch. However if you already consider the first shiny as caught, the second one would be 1 in 512. That is assuming that number to be correct.

Hope this helps!

Comments

Isn't Shiny Chance 1 in 4096 (and use to be 8192 before that)? It only gets lower via other methods (Shiny chance is 1 in 512 in Friend Safari, Halved with shiny charm, decreases even more via SOS, decreases while Masuda Breeding, may lower through ultra warp ride, and a few other ways) :P

Of course most of those aren't in B/W/B2/W2, but what lowers shiny odds to 512 here? Or have I misunderstood?