There's no episode 12 and 13 here. IF you're talking about the wikipedia listing, episodes 1 and 2 aren't split, and the last two episodes neither.

I'm not sure what the reasoning is behind some shows merging two-part episodes, and others not merging them. Like with Under The Dome season 3 episode 1 and 2, I believe they aired right after each other too. But well, that's why the episode number total is off compared to what you expected.