21988729 has 4 divisors (see below), whose sum is σ = 25129984. Its totient is φ = 18847476.

The previous prime is 21988721. The next prime is 21988739. The reversal of 21988729 is 92788912.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21988729 - 2³ = 21988721 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21988721) 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, 1570617 + ... + 1570630.

It is an arithmetic number, because the mean of its divisors is an integer number (6282496).

Almost surely, 2^21988729 is an apocalyptic number.

It is an amenable number.

21988729 is a deficient number, since it is larger than the sum of its proper divisors (3141255).

21988729 is an equidigital number, since it uses as much as digits as its factorization.

21988729 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3141254.

The product of its digits is 145152, while the sum is 46.

The square root of 21988729 is about 4689.2141132603. The cubic root of 21988729 is about 280.1560737017.

The spelling of 21988729 in words is "twenty-one million, nine hundred eighty-eight thousand, seven hundred twenty-nine".