Happy Binary Day !

The last one we'll see in our lifetimes.
111111
That's 63 in decimal.

Although a number of the form 2n - 1, 63 is not a Mersenne prime since n is not prime and 63 is certainly not prime either. It is a Woodall number and a Harshad number. It is a highly cototient number. It is a repdigit in base 4 (333).

I didn't understand any of that.