21724779 has 8 divisors (see below), whose sum is σ = 28999120. Its totient is φ = 14466816.

The previous prime is 21724757. The next prime is 21724783. The reversal of 21724779 is 97742712.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21724779 - 2¹³ = 21716587 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21724739) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 562 + ... + 6615.

It is an arithmetic number, because the mean of its divisors is an integer number (3624890).

Almost surely, 2^21724779 is an apocalyptic number.

21724779 is a deficient number, since it is larger than the sum of its proper divisors (7274341).

21724779 is a wasteful number, since it uses less digits than its factorization.

21724779 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8189.

The product of its digits is 49392, while the sum is 39.

The square root of 21724779 is about 4660.9847671924. The cubic root of 21724779 is about 279.0305717967.

The spelling of 21724779 in words is "twenty-one million, seven hundred twenty-four thousand, seven hundred seventy-nine".