21724429 has 4 divisors (see below), whose sum is σ = 22867840. Its totient is φ = 20581020.

The previous prime is 21724427. The next prime is 21724433. The reversal of 21724429 is 92442712.

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 21724429 - 2¹ = 21724427 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21724429.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21724421) 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, 571677 + ... + 571714.

It is an arithmetic number, because the mean of its divisors is an integer number (5716960).

Almost surely, 2^21724429 is an apocalyptic number.

It is an amenable number.

21724429 is a deficient number, since it is larger than the sum of its proper divisors (1143411).

21724429 is a wasteful number, since it uses less digits than its factorization.

21724429 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1143410.

The product of its digits is 8064, while the sum is 31.

The square root of 21724429 is about 4660.9472213274. The cubic root of 21724429 is about 279.0290733354.

The spelling of 21724429 in words is "twenty-one million, seven hundred twenty-four thousand, four hundred twenty-nine".