21005203840 has 32 divisors (see below), whose sum is σ = 50215566960. Its totient is φ = 8402081280.

The previous prime is 21005203837. The next prime is 21005203841. The reversal of 21005203840 is 4830250012.

It is a tau number, because it is divible by the number of its divisors (32).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005203841) 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 3 ways as a sum of consecutive naturals, for example, 16409676 + ... + 16410955.

Almost surely, 2^21005203840 is an apocalyptic number.

21005203840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21005203840 is an abundant number, since it is smaller than the sum of its proper divisors (29210363120).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21005203840 is an equidigital number, since it uses as much as digits as its factorization.

21005203840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32820650 (or 32820638 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 25.

Adding to 21005203840 its reverse (4830250012), we get a palindrome (25835453852).

The spelling of 21005203840 in words is "twenty-one billion, five million, two hundred three thousand, eight hundred forty".