21515440 has 40 divisors (see below), whose sum is σ = 50429808. Its totient is φ = 8536320.

The previous prime is 21515411. The next prime is 21515449. The reversal of 21515440 is 4451512.

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

It is a hoax number, since the sum of its digits (22) coincides with the sum of the digits of its distinct prime factors.

It is not an unprimeable number, because it can be changed into a prime (21515449) 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, 9454 + ... + 11506.

Almost surely, 2^21515440 is an apocalyptic number.

21515440 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 21515440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25214904).

21515440 is an abundant number, since it is smaller than the sum of its proper divisors (28914368).

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

21515440 is a wasteful number, since it uses less digits than its factorization.

21515440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2197 (or 2191 counting only the distinct ones).

The product of its (nonzero) digits is 800, while the sum is 22.

The square root of 21515440 is about 4638.4738869589. The cubic root of 21515440 is about 278.1314355284.

Adding to 21515440 its reverse (4451512), we get a palindrome (25966952).

The spelling of 21515440 in words is "twenty-one million, five hundred fifteen thousand, four hundred forty".