21729518 has 4 divisors (see below), whose sum is σ = 32594280. Its totient is φ = 10864758.

The previous prime is 21729517. The next prime is 21729527. The reversal of 21729518 is 81592712.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21729511) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5432378 + ... + 5432381.

It is an arithmetic number, because the mean of its divisors is an integer number (8148570).

Almost surely, 2^21729518 is an apocalyptic number.

21729518 is a deficient number, since it is larger than the sum of its proper divisors (10864762).

21729518 is a wasteful number, since it uses less digits than its factorization.

21729518 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10864761.

The product of its digits is 10080, while the sum is 35.

The square root of 21729518 is about 4661.4931084364. The cubic root of 21729518 is about 279.0508593792.

The spelling of 21729518 in words is "twenty-one million, seven hundred twenty-nine thousand, five hundred eighteen".