21020640 has 48 divisors (see below), whose sum is σ = 66216528. Its totient is φ = 5605376.

The previous prime is 21020633. The next prime is 21020641. The reversal of 21020640 is 4602012.

It is a tau number, because it is divible by the number of its divisors (48).

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21020641) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 21417 + ... + 22376.

It is an arithmetic number, because the mean of its divisors is an integer number (1379511).

Almost surely, 2^21020640 is an apocalyptic number.

21020640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21020640 is an abundant number, since it is smaller than the sum of its proper divisors (45195888).

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

21020640 is a wasteful number, since it uses less digits than its factorization.

21020640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 43811 (or 43803 counting only the distinct ones).

The product of its (nonzero) digits is 96, while the sum is 15.

The square root of 21020640 is about 4584.8271505041. The cubic root of 21020640 is about 275.9827756527.

Adding to 21020640 its reverse (4602012), we get a palindrome (25622652).

The spelling of 21020640 in words is "twenty-one million, twenty thousand, six hundred forty".