16720321 has 2 divisors, whose sum is σ = 16720322. Its totient is φ = 16720320.

The previous prime is 16720309. The next prime is 16720349. The reversal of 16720321 is 12302761.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16719921 + 400 = 4089^2 + 20^2 .

It is an emirp because it is prime and its reverse (12302761) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 16720321 - 2⁵ = 16720289 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 16720292 and 16720301.

It is not a weakly prime, because it can be changed into another prime (16720021) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8360160 + 8360161.

It is an arithmetic number, because the mean of its divisors is an integer number (8360161).

Almost surely, 2^16720321 is an apocalyptic number.

It is an amenable number.

16720321 is a deficient number, since it is larger than the sum of its proper divisors (1).

16720321 is an equidigital number, since it uses as much as digits as its factorization.

16720321 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 504, while the sum is 22.

The square root of 16720321 is about 4089.0489114218. The cubic root of 16720321 is about 255.7102893287.

The spelling of 16720321 in words is "sixteen million, seven hundred twenty thousand, three hundred twenty-one".