16921 has 2 divisors, whose sum is σ = 16922. Its totient is φ = 16920.

The previous prime is 16903. The next prime is 16927. The reversal of 16921 is 12961.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15625 + 1296 = 125^2 + 36^2 .

It is a cyclic number.

It is not a de Polignac number, because 16921 - 2⁵ = 16889 is a prime.

It is a Chen prime.

It is an alternating number because its digits alternate between odd and even.

16921 is a lucky number.

It is a nialpdrome in base 12.

It is not a weakly prime, because it can be changed into another prime (16927) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8460 + 8461.

It is an arithmetic number, because the mean of its divisors is an integer number (8461).

2¹⁶⁹²¹ is an apocalyptic number.

It is an amenable number.

16921 is a deficient number, since it is larger than the sum of its proper divisors (1).

16921 is an equidigital number, since it uses as much as digits as its factorization.

16921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 108, while the sum is 19.

The square root of 16921 is about 130.0807441553. The cubic root of 16921 is about 25.6729243939.

It can be divided in two parts, 169 and 21, that added together give a triangular number (190 = T₁₉).

The spelling of 16921 in words is "sixteen thousand, nine hundred twenty-one".