21520540 has 24 divisors (see below), whose sum is σ = 47572560. Its totient is φ = 8155008.

The previous prime is 21520537. The next prime is 21520547. The reversal of 21520540 is 4502512.

It is a Harshad number since it is a multiple of its sum of digits (19).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21520547) 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, 27937 + ... + 28696.

It is an arithmetic number, because the mean of its divisors is an integer number (1982190).

Almost surely, 2^21520540 is an apocalyptic number.

21520540 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21520540 is an abundant number, since it is smaller than the sum of its proper divisors (26052020).

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

21520540 is a wasteful number, since it uses less digits than its factorization.

21520540 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 56661 (or 56659 counting only the distinct ones).

The product of its (nonzero) digits is 400, while the sum is 19.

The square root of 21520540 is about 4639.0236041650. The cubic root of 21520540 is about 278.1534097983.

The spelling of 21520540 in words is "twenty-one million, five hundred twenty thousand, five hundred forty".