199

This number is a prime.

Largest known prime partial sum of Dedekind numbers. Equivalently partial sum of number of monotone Boolean functions of n variables, or partial sums of number of antichains of subsets of an n-set: 2 + 3 + 6 + 20 + 168 = 199 is prime. Curously, the first 5 such partial sums are prime (2, 5, 11, 31, 199), and then no more primes are known. [Post]