[hinkley]

Not that I disagree with you, but a number of these so-called 'prime' hashtable implementations don't actually use prime numbers. They use 'relatively prime' numbers.

If you happened to use 2^n ± 1 you'd have very little bias according to that map, but you wouldn't strictly be using a power of 2.

Unfortunately Java's original hashtable started at 11 and increased using f(m) = 2 * f(m - 1) + 1, giving you 23, 47, 95, 181, etc. Or pretty close to right on the bad parts of the bias curve shown in that link.

Makes me wonder, if Java hashtables had been given a default size of 15 or 7, if this ever would have been fixed...