21008520 has 144 divisors (see below), whose sum is σ = 74643660. Its totient is φ = 5094144.

The previous prime is 21008503. The next prime is 21008521. The reversal of 21008520 is 2580012.

It can be written as a sum of positive squares in 2 ways, for example, as 19554084 + 1454436 = 4422^2 + 1206^2 .

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a junction number, because it is equal to n+sod(n) for n = 21008493 and 21008502.

It is not an unprimeable number, because it can be changed into a prime (21008521) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 313527 + ... + 313593.

Almost surely, 2^21008520 is an apocalyptic number.

21008520 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 21008520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37321830).

21008520 is an abundant number, since it is smaller than the sum of its proper divisors (53635140).

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

21008520 is a wasteful number, since it uses less digits than its factorization.

21008520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 164 (or 90 counting only the distinct ones).

The product of its (nonzero) digits is 160, while the sum is 18.

The square root of 21008520 is about 4583.5052088985. The cubic root of 21008520 is about 275.9297237584.

Adding to 21008520 its reverse (2580012), we get a palindrome (23588532).

It can be divided in two parts, 21008 and 520, that added together give a triangular number (21528 = T₂₀₇).

The spelling of 21008520 in words is "twenty-one million, eight thousand, five hundred twenty".