21001640440 has 128 divisors (see below), whose sum is σ = 52453785600. Its totient is φ = 7503598080.

The previous prime is 21001640437. The next prime is 21001640441. The reversal of 21001640440 is 4404610012.

It is a Harshad number since it is a multiple of its sum of digits (22).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21001640441) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 16419721 + ... + 16420999.

It is an arithmetic number, because the mean of its divisors is an integer number (409795200).

Almost surely, 2^21001640440 is an apocalyptic number.

21001640440 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21001640440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26226892800).

21001640440 is an abundant number, since it is smaller than the sum of its proper divisors (31452145160).

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

21001640440 is a wasteful number, since it uses less digits than its factorization.

21001640440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1925 (or 1921 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 22.

The spelling of 21001640440 in words is "twenty-one billion, one million, six hundred forty thousand, four hundred forty".