20921747840 has 64 divisors (see below), whose sum is σ = 57161216160. Its totient is φ = 7173169152.

The previous prime is 20921747839. The next prime is 20921747857. The reversal of 20921747840 is 4874712902.

It is a tau number, because it is divible by the number of its divisors (64).

It is a junction number, because it is equal to n+sod(n) for n = 20921747791 and 20921747800.

It is a congruent number.

It is an unprimeable number.

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 7 ways as a sum of consecutive naturals, for example, 2330537 + ... + 2339496.

Almost surely, 2^20921747840 is an apocalyptic number.

20921747840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

20921747840 is an abundant number, since it is smaller than the sum of its proper divisors (36239468320).

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

20921747840 is an equidigital number, since it uses as much as digits as its factorization.

20921747840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4670059 (or 4670047 counting only the distinct ones).

The product of its (nonzero) digits is 225792, while the sum is 44.

The spelling of 20921747840 in words is "twenty billion, nine hundred twenty-one million, seven hundred forty-seven thousand, eight hundred forty".