21315440 has 40 divisors (see below), whose sum is σ = 50621760. Its totient is φ = 8343296.

The previous prime is 21315439. The next prime is 21315443. The reversal of 21315440 is 4451312.

It is a tau number, because it is divible by the number of its divisors (40).

It is a Harshad number since it is a multiple of its sum of digits (20).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21315443) by changing a digit.

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, 926 + ... + 6594.

It is an arithmetic number, because the mean of its divisors is an integer number (1265544).

Almost surely, 2^21315440 is an apocalyptic number.

21315440 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 21315440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25310880).

21315440 is an abundant number, since it is smaller than the sum of its proper divisors (29306320).

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

21315440 is a wasteful number, since it uses less digits than its factorization.

21315440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5729 (or 5723 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 20.

The square root of 21315440 is about 4616.8647370266. The cubic root of 21315440 is about 277.2669471485.

Adding to 21315440 its reverse (4451312), we get a palindrome (25766752).

The spelling of 21315440 in words is "twenty-one million, three hundred fifteen thousand, four hundred forty".