The Koide formula is an unexplained relation discovered in 1981. It relates the masses of the three charged leptons so well that it predicted the mass of the tauon.
The Koide formula is:
and the vector
Not only is this result odd in that three apparently random numbers should give a simple fraction, but also that Q is exactly halfway between the two extremes of 1/3 and 1.
This result has never been explained nor understood.