21505523 has 4 divisors (see below), whose sum is σ = 23159808. Its totient is φ = 19851240.

The previous prime is 21505513. The next prime is 21505531. The reversal of 21505523 is 32550512.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21505523 - 2⁴ = 21505507 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21505513) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 827123 + ... + 827148.

It is an arithmetic number, because the mean of its divisors is an integer number (5789952).

Almost surely, 2^21505523 is an apocalyptic number.

21505523 is a deficient number, since it is larger than the sum of its proper divisors (1654285).

21505523 is a wasteful number, since it uses less digits than its factorization.

21505523 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1654284.

The product of its (nonzero) digits is 1500, while the sum is 23.

The square root of 21505523 is about 4637.4047699117. The cubic root of 21505523 is about 278.0886964019.

The spelling of 21505523 in words is "twenty-one million, five hundred five thousand, five hundred twenty-three".