[[15]] is not prime (composite). Want proof? :)

Full prime factorization: [[3]] * [[5]]

Factor pairs:

[[15]] = [[3]] * [[5]]

Proper divisors: [[3]], [[5]]

Primes up to 15: [[2]], [[3]], [[5]], [[7]], [[11]], [[13]].

[[15]] is not a centered hexagonal number.

The closest centered hexagonal numbers are [[7]] (index # [[2]]) and [[19]] (index # [[3]]).

First 20 centered hexagonal numbers: [[1]], [[7]], [[19]], [[37]], [[61]], [[91]], [[127]], [[169]], [[217]], [[271]], [[331]], [[397]], [[469]], [[547]], [[631]], [[721]], [[817]], [[919]], [[1027]], [[1141]].

[[hz/15]] is closest to [[B-1]] at [[15]] Hz (-49 cents).

Note class: [[B]], Octave: [[octave/-1]].

• [[square]]: 225

• [[square root]]: 3.8730

• [[cube]]: 3375

• [[cube root]]: 2.4662

• [[natural log]] (ln): 2.7081

• [[base-10 log]] (log10): 1.1761

• [[base-2 log]] (log2): 3.9069