21505520 has 20 divisors (see below), whose sum is σ = 50000520. Its totient is φ = 8602176.

The previous prime is 21505513. The next prime is 21505531. The reversal of 21505520 is 2550512.

It is a tau number, because it is divible by the number of its divisors (20).

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 = 21505492 and 21505501.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 134330 + ... + 134489.

It is an arithmetic number, because the mean of its divisors is an integer number (2500026).

Almost surely, 2^21505520 is an apocalyptic number.

21505520 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21505520 is an abundant number, since it is smaller than the sum of its proper divisors (28495000).

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

21505520 is a wasteful number, since it uses less digits than its factorization.

21505520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 268832 (or 268826 counting only the distinct ones).

The product of its (nonzero) digits is 500, while the sum is 20.

The square root of 21505520 is about 4637.4044464549. The cubic root of 21505520 is about 278.0886834709.

The spelling of 21505520 in words is "twenty-one million, five hundred five thousand, five hundred twenty".