A093599: Composite numbers having an odd number of prime factors, all of which are distinct.

High-pitched and consistently noisy.

Residue counts:
2   [101283, 124076]
3   [75926, 74837, 74596]
4   [0, 62004, 101283, 62072]
5   [50647, 43786, 43548, 43693, 43685]
6   [25392, 36870, 37924, 50534, 37967, 36672]
7   [37962, 31279, 31328, 31192, 31210, 31190, 31198]
8   [0, 31101, 50647, 31021, 0, 30903, 50636, 31051]
9   [0, 24871, 24912, 37958, 24996, 24772, 37968, 24970, 24912]
10   [16945, 22635, 21023, 22609, 21080, 33702, 21151, 22525, 21084, 22605]
11   [25342, 20090, 19958, 19945, 19948, 20054, 20014, 20049, 20102, 19943, 19914]
12   [0, 18455, 37924, 25295, 0, 18310, 25392, 18415, 0, 25239, 37967, 18362]


First 100 first differences:
[12, 24, 4, 8, 24, 3, 5, 4, 16, 8, 16, 11, 5, 4, 8, 4, 4, 5, 27, 8, 1, 7, 8, 
 9, 3, 8, 7, 9, 3, 1, 4, 20, 8, 4, 23, 9, 3, 9, 4, 4, 11, 14, 3, 4, 4, 8, 8, 
 3, 1, 4, 1, 3, 4, 13, 10, 5, 4, 9, 11, 4, 8, 12, 12, 4, 21, 6, 13, 8, 8, 5, 
 3, 4, 4, 3, 1, 5, 3, 9, 11, 4, 3, 1, 5, 3, 4, 5, 2, 5, 8, 4, 23, 5, 5, 15, 
 11, 1, 12, 5, 3, 15]

First 99 second differences:
[12,-20,4,16,-21,2,-1,12,-8,8,-5,-6,-1,4,-4,0,1,22,-19,-7,6,1,1,-6,5,-1,2,
 -6,-2,3,16,-12,-4,19,-14,-6,6,-5,0,7,3,-11,1,0,4,0,-5,-2,3,-3,2,1,9,-3,-5,
 -1,5,2,-7,4,4,0,-8,17,-15,7,-5,0,-3,-2,1,0,-1,-2,4,-2,6,2,-7,-1,-2,4,-2,1,1,
 -3,3,3,-4,19,-18,0,10,-4,-10,11,-7,-2,12]

Two spectral lines stand out at 44100/9=4900Hz and 44100/4=11025Hz. 
There are no numbers congruent to 0 mod 4, 8, or 9
because they are all powers of a prime number. So, any number that is 
divisible by 4, 8, or 9 would have at least 2 non-distinct prime factors. 


--David Oh