I found this li'l equation:
The formula for the probability of finding a Shiny Pokémon. Nc is the number of Pokémon in the chain, up to 40. The chances are calculated so that any shaking patch found in or after a chain of 40 has a 1 in 200 probability of being Shiny. ~ Bulbapedia
I tried to figure this out, and the result I got was about a one in five chance of finding the Shiny, and I knew that wasn't right. If anyone is willing to figure this out, feel free to edit it in or post a comment so I can edit it in. :3
So, inserting 2 as Nc, you would get this equation:
Which would be 0.00014346415.
Our next step would be to convert it to a fraction, then simplify it.
Original fraction = 143464/1000000000
Simplified fraction = 17933/125000000
So it looks to be pretty close to the normal chances of finding a Shiny, which is very rare. Congratulations on finding one! ;)
Hope we helped. :)
@Jaja, learn to spell the word Solumni. And stupid. Seriously. o_o'