21002540821 has 4 divisors (see below), whose sum is σ = 21003559200. Its totient is φ = 21001522444.

The previous prime is 21002540807. The next prime is 21002540831. The reversal of 21002540821 is 12804520012.

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 21002540821 - 2⁷ = 21002540693 is a prime.

It is a super-2 number, since 2×21002540821² (a number of 21 digits) 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 (21002540831) 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, 477601 + ... + 519718.

It is an arithmetic number, because the mean of its divisors is an integer number (5250889800).

Almost surely, 2^21002540821 is an apocalyptic number.

It is an amenable number.

21002540821 is a deficient number, since it is larger than the sum of its proper divisors (1018379).

21002540821 is an equidigital number, since it uses as much as digits as its factorization.

21002540821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1018378.

The product of its (nonzero) digits is 1280, while the sum is 25.

The spelling of 21002540821 in words is "twenty-one billion, two million, five hundred forty thousand, eight hundred twenty-one".