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

Full prime factorization: [[2]] * [[2]] * [[5]]

Factor pairs:

[[20]] = [[2]] * [[10]]

[[20]] = [[4]] * [[5]]

Proper divisors: [[2]], [[4]], [[5]], [[10]]

Primes up to 20: [[2]], [[3]], [[5]], [[7]], [[11]], [[13]], [[17]], [[19]].

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

The closest centered hexagonal numbers are [[19]] (index # [[3]]) and [[37]] (index # [[4]]).

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/20]] is closest to [[D#0]] at [[20]] Hz (+49 cents).

Note class: [[D#]], Octave: [[octave/0]].

• [[square]]: 400

• [[square root]]: 4.4721

• [[cube]]: 8000

• [[cube root]]: 2.7144

• [[natural log]] (ln): 2.9957

• [[base-10 log]] (log10): 1.3010

• [[base-2 log]] (log2): 4.3219