16920821 has 2 divisors, whose sum is σ = 16920822. Its totient is φ = 16920820.

The previous prime is 16920817. The next prime is 16920859. The reversal of 16920821 is 12802961.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16728100 + 192721 = 4090^2 + 439^2 .

It is an emirp because it is prime and its reverse (12802961) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 16920821 - 2² = 16920817 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (16920221) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8460410 + 8460411.

It is an arithmetic number, because the mean of its divisors is an integer number (8460411).

Almost surely, 2^16920821 is an apocalyptic number.

It is an amenable number.

16920821 is a deficient number, since it is larger than the sum of its proper divisors (1).

16920821 is an equidigital number, since it uses as much as digits as its factorization.

16920821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1728, while the sum is 29.

The square root of 16920821 is about 4113.4925549951. The cubic root of 16920821 is about 256.7283386594.

The spelling of 16920821 in words is "sixteen million, nine hundred twenty thousand, eight hundred twenty-one".