21208520 has 32 divisors (see below), whose sum is σ = 50527800. Its totient is φ = 7984128.

The previous prime is 21208513. The next prime is 21208531. The reversal of 21208520 is 2580212.

It can be written as a sum of positive squares in 4 ways, for example, as 15225604 + 5982916 = 3902^2 + 2446^2 .

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

It is a junction number, because it is equal to n+sod(n) for n = 21208492 and 21208501.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 14915 + ... + 16274.

Almost surely, 2^21208520 is an apocalyptic number.

21208520 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21208520 is an abundant number, since it is smaller than the sum of its proper divisors (29319280).

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

21208520 is a wasteful number, since it uses less digits than its factorization.

21208520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 31217 (or 31213 counting only the distinct ones).

The product of its (nonzero) digits is 320, while the sum is 20.

The square root of 21208520 is about 4605.2708932266. The cubic root of 21208520 is about 276.8025718963.

Adding to 21208520 its reverse (2580212), we get a palindrome (23788732).

The spelling of 21208520 in words is "twenty-one million, two hundred eight thousand, five hundred twenty".