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

Full prime factorization: [[2]] * [[2]] * [[7]]

Factor pairs:

[[28]] = [[2]] * [[14]]

[[28]] = [[4]] * [[7]]

Proper divisors: [[2]], [[4]], [[7]], [[14]]

Primes up to 28: [[2]], [[3]], [[5]], [[7]], [[11]], [[13]], [[17]], [[19]], [[23]].

[[28]] 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/28]] is closest to [[A0]] at [[28]] Hz (+31 cents).

Note class: [[A]], Octave: [[octave/0]].

• [[square]]: 784

• [[square root]]: 5.2915

• [[cube]]: 21952

• [[cube root]]: 3.0366

• [[natural log]] (ln): 3.3322

• [[base-10 log]] (log10): 1.4472

• [[base-2 log]] (log2): 4.8074