21729171 has 12 divisors (see below), whose sum is σ = 29940936. Its totient is φ = 14016960.

The previous prime is 21729161. The next prime is 21729199. The reversal of 21729171 is 17192712.

It is a happy number.

It is not a de Polignac number, because 21729171 - 2⁹ = 21728659 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21729131) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 886 + ... + 6651.

It is an arithmetic number, because the mean of its divisors is an integer number (2495078).

Almost surely, 2^21729171 is an apocalyptic number.

21729171 is a deficient number, since it is larger than the sum of its proper divisors (8211765).

21729171 is an equidigital number, since it uses as much as digits as its factorization.

21729171 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7602 (or 7571 counting only the distinct ones).

The product of its digits is 1764, while the sum is 30.

The square root of 21729171 is about 4661.4558884537. The cubic root of 21729171 is about 279.0493739779.

The spelling of 21729171 in words is "twenty-one million, seven hundred twenty-nine thousand, one hundred seventy-one".