21231520 has 24 divisors (see below), whose sum is σ = 50159844. Its totient is φ = 8492544.

The previous prime is 21231503. The next prime is 21231523. The reversal of 21231520 is 2513212.

It can be written as a sum of positive squares in 2 ways, for example, as 17405584 + 3825936 = 4172^2 + 1956^2 .

It is a Harshad number since it is a multiple of its sum of digits (16).

It is a junction number, because it is equal to n+sod(n) for n = 21231494 and 21231503.

It is not an unprimeable number, because it can be changed into a prime (21231523) 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 3 ways as a sum of consecutive naturals, for example, 66189 + ... + 66508.

Almost surely, 2^21231520 is an apocalyptic number.

21231520 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21231520 is an abundant number, since it is smaller than the sum of its proper divisors (28928324).

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

21231520 is a wasteful number, since it uses less digits than its factorization.

21231520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 132712 (or 132704 counting only the distinct ones).

The product of its (nonzero) digits is 120, while the sum is 16.

The square root of 21231520 is about 4607.7673552383. The cubic root of 21231520 is about 276.9025970926.

Adding to 21231520 its reverse (2513212), we get a palindrome (23744732).

The spelling of 21231520 in words is "twenty-one million, two hundred thirty-one thousand, five hundred twenty".