20821901 has 4 divisors (see below), whose sum is σ = 20843904. Its totient is φ = 20799900.

The previous prime is 20821897. The next prime is 20821907. The reversal of 20821901 is 10912802.

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 20821901 - 2² = 20821897 is a prime.

It is a super-2 number, since 2×20821901² = 867103122507602, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20821907) 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, 9515 + ... + 11496.

It is an arithmetic number, because the mean of its divisors is an integer number (5210976).

Almost surely, 2^20821901 is an apocalyptic number.

It is an amenable number.

20821901 is a deficient number, since it is larger than the sum of its proper divisors (22003).

20821901 is an equidigital number, since it uses as much as digits as its factorization.

20821901 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22002.

The product of its (nonzero) digits is 288, while the sum is 23.

The square root of 20821901 is about 4563.1021246516. The cubic root of 20821901 is about 275.1102632213.

Subtracting from 20821901 its reverse (10912802), we obtain a palindrome (9909099).

The spelling of 20821901 in words is "twenty million, eight hundred twenty-one thousand, nine hundred one".