21015400 has 96 divisors (see below), whose sum is σ = 59192640. Its totient is φ = 6773760.

The previous prime is 21015391. The next prime is 21015403. The reversal of 21015400 is 451012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21015403) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 23359 + ... + 24241.

It is an arithmetic number, because the mean of its divisors is an integer number (616590).

Almost surely, 2^21015400 is an apocalyptic number.

21015400 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 21015400, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29596320).

21015400 is an abundant number, since it is smaller than the sum of its proper divisors (38177240).

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

21015400 is a wasteful number, since it uses less digits than its factorization.

21015400 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 923 (or 914 counting only the distinct ones).

The product of its (nonzero) digits is 40, while the sum is 13.

The square root of 21015400 is about 4584.2556647726. The cubic root of 21015400 is about 275.9598415282.

Adding to 21015400 its reverse (451012), we get a palindrome (21466412).

The spelling of 21015400 in words is "twenty-one million, fifteen thousand, four hundred".