20730821 has 4 divisors (see below), whose sum is σ = 20790912. Its totient is φ = 20670732.

The previous prime is 20730799. The next prime is 20730823. The reversal of 20730821 is 12803702.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 20730821 - 2⁶ = 20730757 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20730823) 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 3 ways as a sum of consecutive naturals, for example, 29525 + ... + 30218.

It is an arithmetic number, because the mean of its divisors is an integer number (5197728).

Almost surely, 2^20730821 is an apocalyptic number.

It is an amenable number.

20730821 is a deficient number, since it is larger than the sum of its proper divisors (60091).

20730821 is an equidigital number, since it uses as much as digits as its factorization.

20730821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 60090.

The product of its (nonzero) digits is 672, while the sum is 23.

The square root of 20730821 is about 4553.1111341587. Note that the first 4 decimals coincide. The cubic root of 20730821 is about 274.7085441052.

The spelling of 20730821 in words is "twenty million, seven hundred thirty thousand, eight hundred twenty-one".