21015705171 has 4 divisors (see below), whose sum is σ = 28020940232. Its totient is φ = 14010470112.

The previous prime is 21015705157. The next prime is 21015705211. The reversal of 21015705171 is 17150751012.

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

It is not a de Polignac number, because 21015705171 - 2⁷ = 21015705043 is a prime.

It is a super-2 number, since 2×21015705171² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21015705121) 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, 3502617526 + ... + 3502617531.

It is an arithmetic number, because the mean of its divisors is an integer number (7005235058).

Almost surely, 2^21015705171 is an apocalyptic number.

21015705171 is a deficient number, since it is larger than the sum of its proper divisors (7005235061).

21015705171 is an equidigital number, since it uses as much as digits as its factorization.

21015705171 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7005235060.

The product of its (nonzero) digits is 2450, while the sum is 30.

The spelling of 21015705171 in words is "twenty-one billion, fifteen million, seven hundred five thousand, one hundred seventy-one".