21523871 has 4 divisors (see below), whose sum is σ = 21543192. Its totient is φ = 21504552.

The previous prime is 21523847. The next prime is 21523891. The reversal of 21523871 is 17832512.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21523871 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21523891) 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, 7880 + ... + 10253.

It is an arithmetic number, because the mean of its divisors is an integer number (5385798).

Almost surely, 2^21523871 is an apocalyptic number.

21523871 is a deficient number, since it is larger than the sum of its proper divisors (19321).

21523871 is a wasteful number, since it uses less digits than its factorization.

21523871 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19320.

The product of its digits is 3360, while the sum is 29.

The square root of 21523871 is about 4639.3826097876. The cubic root of 21523871 is about 278.1677601385.

The spelling of 21523871 in words is "twenty-one million, five hundred twenty-three thousand, eight hundred seventy-one".