20821001 has 4 divisors (see below), whose sum is σ = 20830992. Its totient is φ = 20811012.

The previous prime is 20820977. The next prime is 20821007. The reversal of 20821001 is 10012802.

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, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 10012802 = 2 ⋅5006401.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20821001 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20821007) 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, 551 + ... + 6476.

It is an arithmetic number, because the mean of its divisors is an integer number (5207748).

Almost surely, 2^20821001 is an apocalyptic number.

It is an amenable number.

20821001 is a deficient number, since it is larger than the sum of its proper divisors (9991).

20821001 is an equidigital number, since it uses as much as digits as its factorization.

20821001 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9990.

The product of its (nonzero) digits is 32, while the sum is 14.

The square root of 20821001 is about 4563.0035064637. The cubic root of 20821001 is about 275.1062994013.

Subtracting from 20821001 its product of nonzero digits (32), we obtain a square (20820969 = 4563²).

Adding to 20821001 its reverse (10012802), we get a palindrome (30833803).

The spelling of 20821001 in words is "twenty million, eight hundred twenty-one thousand, one".