I added two more sound files to my page of integer sequence noise. The new sequences are the palindromic numbers (like 121, 32423, etc.) and the set of values taken on by sigma, the sum of divisors function (1,3,4,6,7,8,12,13,14, etc.). The first doesn't sound very interesting, as palindromic numbers are a bit too rare and regular, but the second one is quite noisy. There is a bit of a peak at 44100/6=7350 hz, since multiples of 6 tend to be values of the sum of divisors function, but it's pretty uniformly noisy.