20720821 has 8 divisors (see below), whose sum is σ = 22644000. Its totient is φ = 18804240.

The previous prime is 20720789. The next prime is 20720893. The reversal of 20720821 is 12802702.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 20720821 - 2⁵ = 20720789 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 20720792 and 20720801.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20720221) 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 in 7 ways as a sum of consecutive naturals, for example, 6855 + ... + 9403.

It is an arithmetic number, because the mean of its divisors is an integer number (2830500).

Almost surely, 2^20720821 is an apocalyptic number.

It is an amenable number.

20720821 is a deficient number, since it is larger than the sum of its proper divisors (1923179).

20720821 is a wasteful number, since it uses less digits than its factorization.

20720821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3299.

The product of its (nonzero) digits is 448, while the sum is 22.

The square root of 20720821 is about 4552.0128514757. The cubic root of 20720821 is about 274.6643662879.

The spelling of 20720821 in words is "twenty million, seven hundred twenty thousand, eight hundred twenty-one".