A154389: Nonprimes whose largest digit is an odd nonprime.

Rhythmic, with sections of 9 beats followed by short pauses of static noise.

Residue counts:
2   [925986, 1025677]
3   [709907, 620881, 620875]
4   [447562, 510193, 478424, 515484]
5   [370432, 338188, 338145, 337843, 567055]
6   [308662, 312219, 308662, 401245, 308662, 312213]
7   [304246, 274661, 274615, 274584, 274569, 274425, 274563]
8   [222066, 255472, 239212, 257819, 225496, 254721, 239212, 257665]
9   [236622, 207088, 206969, 236657, 206875, 206968, 236628, 206918, 206938]
10   [185248, 153004, 185185, 152659, 185185, 185184, 185184, 152960, 185184, 381870]
11   [193622, 175864, 175742, 175889, 175725, 175752, 175724, 175814, 175907, 175794, 175830]
12   [149187, 154716, 159474, 200622, 149187, 154854, 159475, 157503, 149188, 200623, 159475, 157359]

First 100 first differences:
[8, 1, 29, 10, 20, 21, 1, 1, 1, 1, 1, 1, 2, 1, 1, 10, 1, 8, 10, 30, 10, 20, 1, 2, 
 2, 1, 1, 2, 11, 10, 30, 10, 20, 10, 1, 1, 1, 2, 1, 1, 1, 1, 1, 10, 10, 10, 10, 30, 
 21, 1, 1, 1, 1, 1, 1, 2, 1, 30, 30, 10, 20, 1, 2, 1, 1, 1, 1, 1, 1, 21, 10, 10, 10,
 10, 20, 10, 1, 1, 1, 2, 1, 1, 1, 1, 11, 20, 10, 10, 20, 10, 10, 1, 2, 1, 1, 1, 1, 
 1, 1, 1]

First 99 second differences:
[-7,28,-19,10,1,-20,0,0,0,0,0,1,-1,0,9,-9,7,2,20,-20,10,-19,1,0,-1,0,1,9,-1,
 20,-20,10,-10,-9,0,0,1,-1,0,0,0,0,9,0,0,0,20,-9,-20,0,0,0,0,0,1,-1,29,0,-20,
 10,-19,1,-1,0,0,0,0,0,20,-11,0,0,0,10,-10,-9,0,0,1,-1,0,0,0,10,9,-10,0,10,-10,
 0,-9,1,-1,0,0,0,0,0,0]

The spectrum has lines at around 4410Hz, 8820Hz, 13120Hz, and 17500Hz
which roughly correspond to 44100/10, 44100/5, 44100/3.33, and 44100/2.5, each
of which divides 10 into an integer. This is likely related to the sequence being
based on digits. Then, there is a smaller line at around 14700Hz which corresponds
to 44100/3. 

The only digits that are a odd nonprime are 1 or 9. So, in large sections where
each consecutive number must have a 9 such as the 9 millions, the sequence becomes 
the same as the nonprimes as 9 would always be the largest digit. In addition, we 
can see that there are more numbers that are congruent to 4 mod 5 or congruent to 
9 mod 10. This is because any number that ends in 9 automatically meets the 
requirement of having its largest number be an odd nonprime.


-- David Oh