A005214: Triangular numbers together with squares (excluding 0).

Can hear a similar "winding down" in pitch similar to 
A000217 (triangular numbers) and A000290 (square numbers)
with a more crackly sound.

Residue counts:
2   [1204, 1205]
3   [1273, 1136, 0]
4   [850, 851, 354, 354]
5   [763, 963, 0, 283, 400]
6   [634, 566, 0, 639, 570, 0]
7   [544, 687, 286, 404, 286, 0, 202]
8   [425, 675, 177, 177, 425, 176, 177, 177]
9   [645, 692, 0, 314, 222, 0, 314, 222, 0]
10   [381, 482, 0, 141, 200, 382, 481, 0, 142, 200]
11   [346, 438, 0, 437, 310, 182, 257, 0, 0, 182, 257]
12   [398, 448, 0, 236, 452, 0, 236, 118, 0, 403, 118, 0]

First 100 first differences:
[2, 1, 2, 3, 1, 5, 1, 5, 4, 3, 8, 9, 4, 6, 9, 2, 12, 3, 10, 
 9, 5, 15, 1, 15, 8, 9, 16, 2, 19, 6, 14, 15, 6, 22, 3, 20, 
 13, 11, 24, 1, 26, 10, 17, 22, 6, 29, 6, 24, 19, 12, 32, 1, 
 32, 15, 19, 30, 5, 36, 10, 27, 26, 12, 39, 4, 36, 21, 20, 39, 
 3, 43, 15, 29, 34, 11, 46, 8, 39, 28, 20, 49, 50, 21, 30, 43, 
 9, 53, 13, 41, 36, 19, 56, 4, 53, 28, 30, 53, 6, 60, 19, 42]

First 99 second differences:
[-1,1,1,-2,4,-4,4,-1,-1,5,1,-5,2,3,-7,10,-9,7,-1,-4,10,-14,14,
 -7,1,7,-14,17,-13,8,1,-9,16,-19,17,-7,-2,13,-23,25,-16,7,5,-16,
 23,-23,18,-5,-7,20,-31,31,-17,4,11,-25,31,-26,17,-1,-14,27,-35,
 32,-15,-1,19,-36,40,-28,14,5,-23,35,-38,31,-11,-8,29,1,-29,9,13,
 -34,44,-40,28,-5,-17,37,-52,49,-25,2,23,-47,54,-41,23]

The spectrogram has a similar shape to the spectrograms for 
A000217 (triangular numbers) and A000290 (square numbers)
while being noisier and having a rougher texture. 


-- David Oh