21729825 has 144 divisors (see below), whose sum is σ = 48746880. Its totient is φ = 9123840.

The previous prime is 21729821. The next prime is 21729889. The reversal of 21729825 is 52892712.

It is not a de Polignac number, because 21729825 - 2² = 21729821 is a prime.

Its product of digits (20160) is a multiple of the sum of its prime divisors (80).

It is a self number, because there is not a number n which added to its sum of digits gives 21729825.

It is not an unprimeable number, because it can be changed into a prime (21729821) by changing a digit.

It is a polite number, since it can be written in 143 ways as a sum of consecutive naturals, for example, 944764 + ... + 944786.

It is an arithmetic number, because the mean of its divisors is an integer number (338520).

Almost surely, 2^21729825 is an apocalyptic number.

21729825 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21729825 is an abundant number, since it is smaller than the sum of its proper divisors (27017055).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21729825 is a wasteful number, since it uses less digits than its factorization.

21729825 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 88 (or 80 counting only the distinct ones).

The product of its digits is 20160, while the sum is 36.

The square root of 21729825 is about 4661.5260376834. The cubic root of 21729825 is about 279.0521735396.

The spelling of 21729825 in words is "twenty-one million, seven hundred twenty-nine thousand, eight hundred twenty-five".