A005153: Practical numbers: positive integers m such that every k <= sigma(m) is
a sum of distinct divisors of m. Also called panarithmic numbers.

High-pitched frequency stands out clearly with lower-pitched static.


Residue counts:
2   [97384, 1]
3   [62520, 17428, 17437]
4   [74903, 1, 22481, 0]
5   [36285, 15291, 15273, 15281, 15255]
6   [62520, 1, 17437, 0, 17427, 0]
7   [28100, 11566, 11532, 11539, 11547, 11548, 11553]
8   [50571, 1, 11241, 0, 24332, 0, 11240, 0]
9   [29547, 5829, 5800, 16470, 5793, 5809, 16503, 5806, 5828]
10   [36285, 1, 15273, 0, 15255, 0, 15290, 0, 15281, 0]
11   [17482, 7974, 7998, 7995, 8025, 7982, 7990, 7971, 7981, 7981, 8006]
12   [40040, 1, 1, 0, 17427, 0, 22480, 0, 17436, 0, 0, 0]

Density information:
A(x) at x=10,100,1000,...:
[5, 30, 198, 1456, 11751, 97385]

A(x)/x at x=10,100,1000,...:
0.5,0.3,0.198,0.1456,0.11751,0.097385,

First 100 first differences:
[1, 2, 2, 2, 4, 4, 2, 2, 4, 4, 2, 2, 4, 4, 2, 6, 6, 2, 4, 4, 2, 6, 6, 2, 4,
 4, 2, 6, 4, 4, 4, 4, 8, 6, 2, 4, 8, 4, 6, 6, 4, 2, 6, 8, 4, 12, 4, 2, 2, 4,
 4, 2, 6, 4, 4, 4, 6, 6, 12, 4, 4, 4, 6, 2, 4, 4, 8, 6, 6, 4, 2, 2, 4, 8, 4, 6, 
 6, 4, 2, 6, 4, 8, 4, 4, 10, 2, 4, 6, 2, 4, 4, 8, 6, 2, 4, 12, 8, 8, 2, 6]

First 99 second differences:
[1,0,0,2,0,-2,0,2,0,-2,0,2,0,-2,4,0,-4,2,0,-2,4,0,-4,2,0,-2,4,-2,0,0,0,4,
 -2,-4,2,4,-4,2,0,-2,-2,4,2,-4,8,-8,-2,0,2,0,-2,4,-2,0,0,2,0,6,-8,0,0,2,-4,
 2,0,4,-2,0,-2,-2,0,2,4,-4,2,0,-2,-2,4,-2,4,-4,0,6,-8,2,2,-4,2,0,4,-2,-4,2,8,
 -4,0,-6,4]

The 2 strongest lines stand out at 7350Hz and 11025Hz. These correspond
to 44100/6 and 44100/4.


-- David Oh