21020940 has 72 divisors (see below), whose sum is σ = 65978640. Its totient is φ = 5410944.

The previous prime is 21020927. The next prime is 21020941. The reversal of 21020940 is 4902012.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21020941) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 3207 + ... + 7233.

It is an arithmetic number, because the mean of its divisors is an integer number (916370).

Almost surely, 2^21020940 is an apocalyptic number.

21020940 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 21020940, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32989320).

21020940 is an abundant number, since it is smaller than the sum of its proper divisors (44957700).

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

21020940 is a wasteful number, since it uses less digits than its factorization.

21020940 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4071 (or 4066 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 18.

The square root of 21020940 is about 4584.8598669970. The cubic root of 21020940 is about 275.9840885597.

Adding to 21020940 its reverse (4902012), we get a palindrome (25922952).

The spelling of 21020940 in words is "twenty-one million, twenty thousand, nine hundred forty".