21311520 has 96 divisors (see below), whose sum is σ = 69491520. Its totient is φ = 5483520.

The previous prime is 21311503. The next prime is 21311527. The reversal of 21311520 is 2511312.

It is a tau number, because it is divible by the number of its divisors (96).

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

It is a self number, because there is not a number n which added to its sum of digits gives 21311520.

It is not an unprimeable number, because it can be changed into a prime (21311527) 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 15 ways as a sum of consecutive naturals, for example, 13155 + ... + 14685.

It is an arithmetic number, because the mean of its divisors is an integer number (723870).

Almost surely, 2^21311520 is an apocalyptic number.

21311520 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 21311520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34745760).

21311520 is an abundant number, since it is smaller than the sum of its proper divisors (48180000).

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

21311520 is a wasteful number, since it uses less digits than its factorization.

21311520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1578 (or 1570 counting only the distinct ones).

The product of its (nonzero) digits is 60, while the sum is 15.

The square root of 21311520 is about 4616.4401869839. The cubic root of 21311520 is about 277.2499492498.

Adding to 21311520 its reverse (2511312), we get a palindrome (23822832).

The spelling of 21311520 in words is "twenty-one million, three hundred eleven thousand, five hundred twenty".