20821811 has 4 divisors (see below), whose sum is σ = 20954592. Its totient is φ = 20689032.

The previous prime is 20821789. The next prime is 20821841. The reversal of 20821811 is 11812802.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 20821811 - 2⁶ = 20821747 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20821841) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 66155 + ... + 66468.

It is an arithmetic number, because the mean of its divisors is an integer number (5238648).

Almost surely, 2^20821811 is an apocalyptic number.

20821811 is a deficient number, since it is larger than the sum of its proper divisors (132781).

20821811 is a wasteful number, since it uses less digits than its factorization.

20821811 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 132780.

The product of its (nonzero) digits is 256, while the sum is 23.

The square root of 20821811 is about 4563.0922629287. The cubic root of 20821811 is about 275.1098668444.

Subtracting from 20821811 its reverse (11812802), we obtain a palindrome (9009009).

The spelling of 20821811 in words is "twenty million, eight hundred twenty-one thousand, eight hundred eleven".