The Kemeny constant of a Markov chain

Given an ergodic finite-state Markov chain, let M_{iw} denote the mean time from i to equilibrium, meaning the expected time, starting from i, to arrive at a state selected randomly according to the equilibrium measure w of the chain. John Kemeny observed that M_{iw} does not depend on starting the point i. The common value K=M_{iw} is the Kemeny constant or seek time of the chain. K is a spectral invariant, to wit, the trace of the resolvent matrix. We review basic facts about the seek time, and connect it to the bus paradox and the Central Limit Theorem for ergodic Markov chains.