21715571 has 4 divisors (see below), whose sum is σ = 22039752. Its totient is φ = 21391392.

The previous prime is 21715541. The next prime is 21715621. The reversal of 21715571 is 17551712.

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 21715571 - 2¹⁰ = 21714547 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21715541) 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, 161990 + ... + 162123.

It is an arithmetic number, because the mean of its divisors is an integer number (5509938).

Almost surely, 2^21715571 is an apocalyptic number.

21715571 is a deficient number, since it is larger than the sum of its proper divisors (324181).

21715571 is an equidigital number, since it uses as much as digits as its factorization.

21715571 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 324180.

The product of its digits is 2450, while the sum is 29.

The square root of 21715571 is about 4659.9968884110. The cubic root of 21715571 is about 278.9911440601.

Adding to 21715571 its sum of digits (29), we get a square (21715600 = 4660²).

The spelling of 21715571 in words is "twenty-one million, seven hundred fifteen thousand, five hundred seventy-one".