820521021 has 16 divisors (see below), whose sum is σ = 1143498240. Its totient is φ = 522358320.

The previous prime is 820521019. The next prime is 820521029. The reversal of 820521021 is 120125028.

It is a happy number.

It is not a de Polignac number, because 820521021 - 2¹ = 820521019 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (820521029) 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 15 ways as a sum of consecutive naturals, for example, 33106 + ... + 52316.

It is an arithmetic number, because the mean of its divisors is an integer number (71468640).

Almost surely, 2^820521021 is an apocalyptic number.

It is an amenable number.

820521021 is a deficient number, since it is larger than the sum of its proper divisors (322977219).

820521021 is a wasteful number, since it uses less digits than its factorization.

820521021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19856.

The product of its (nonzero) digits is 320, while the sum is 21.

The square root of 820521021 is about 28644.7381031840. The cubic root of 820521021 is about 936.1883603952.

Adding to 820521021 its reverse (120125028), we get a palindrome (940646049).

The spelling of 820521021 in words is "eight hundred twenty million, five hundred twenty-one thousand, twenty-one".