821000021 has 4 divisors (see below), whose sum is σ = 822158700. Its totient is φ = 819841344.

The previous prime is 821000017. The next prime is 821000027. The reversal of 821000021 is 120000128.

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

It can be written as a sum of positive squares in 2 ways, for example, as 401200900 + 419799121 = 20030^2 + 20489^2 .

It is a cyclic number.

It is not a de Polignac number, because 821000021 - 2² = 821000017 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (821000027) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 578276 + ... + 579693.

It is an arithmetic number, because the mean of its divisors is an integer number (205539675).

Almost surely, 2^821000021 is an apocalyptic number.

It is an amenable number.

821000021 is a deficient number, since it is larger than the sum of its proper divisors (1158679).

821000021 is a wasteful number, since it uses less digits than its factorization.

821000021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1158678.

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

The square root of 821000021 is about 28653.0979302413. The cubic root of 821000021 is about 936.3704995401.

Adding to 821000021 its reverse (120000128), we get a palindrome (941000149).

The spelling of 821000021 in words is "eight hundred twenty-one million, twenty-one", and thus it is an aban number.