20808821 has 4 divisors (see below), whose sum is σ = 22700544. Its totient is φ = 18917100.

The previous prime is 20808803. The next prime is 20808829. The reversal of 20808821 is 12880802.

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 20808821 - 2¹⁰ = 20807797 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 (20808829) 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, 945845 + ... + 945866.

It is an arithmetic number, because the mean of its divisors is an integer number (5675136).

Almost surely, 2^20808821 is an apocalyptic number.

It is an amenable number.

20808821 is a deficient number, since it is larger than the sum of its proper divisors (1891723).

20808821 is a wasteful number, since it uses less digits than its factorization.

20808821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1891722.

The product of its (nonzero) digits is 2048, while the sum is 29.

The square root of 20808821 is about 4561.6686639869. The cubic root of 20808821 is about 275.0526444668.

It can be divided in two parts, 2080 and 8821, that added together give a palindrome (10901).

The spelling of 20808821 in words is "twenty million, eight hundred eight thousand, eight hundred twenty-one".