21729388 has 48 divisors (see below), whose sum is σ = 43223040. Its totient is φ = 9504000.

The previous prime is 21729377. The next prime is 21729391. The reversal of 21729388 is 88392712.

It is a self number, because there is not a number n which added to its sum of digits gives 21729388.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 53988 + ... + 54388.

It is an arithmetic number, because the mean of its divisors is an integer number (900480).

Almost surely, 2^21729388 is an apocalyptic number.

It is an amenable number.

21729388 is a deficient number, since it is larger than the sum of its proper divisors (21493652).

21729388 is a wasteful number, since it uses less digits than its factorization.

21729388 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 478 (or 476 counting only the distinct ones).

The product of its digits is 48384, while the sum is 40.

The square root of 21729388 is about 4661.4791643855. The cubic root of 21729388 is about 279.0503028907.

The spelling of 21729388 in words is "twenty-one million, seven hundred twenty-nine thousand, three hundred eighty-eight".