Recursive (n choose 2) is my favorite. https://oeis.org/A086714 https://oeis.org/A086714 If you think about it, it quantifies emergence of harmonic interferen

Recursive (n choose 2) is my favorite. https://oeis.org/A086714 https://oeis.org/A086714 If you think about it, it quantifies emergence of harmonic interference in the superposition of 4 distinct waveforms. If those waveforms happen to have irrational wavelengths (wrt. each other), their combination will never be in the same state twice. This obviously has implications for pseudorandomness, etc.