If you read the cites on that link, you'll see that the value for 26 was only added in 2016. They do not have a closed form formula, or they would have shown it.
I mean, they could just be slow revealing. I doubt it, though.
Fair enough. I was obviously reading the above as having a polynomial time as having an efficient time one. Where efficient was shorthand for "quick." Both leaps, I concede were misguided.