21724720 has 40 divisors (see below), whose sum is σ = 50706576. Its totient is φ = 8656128.

The previous prime is 21724663. The next prime is 21724721. The reversal of 21724720 is 2742712.

It is a tau number, because it is divible by the number of its divisors (40).

It is not an unprimeable number, because it can be changed into a prime (21724721) 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 in 7 ways as a sum of consecutive naturals, for example, 35134 + ... + 35746.

Almost surely, 2^21724720 is an apocalyptic number.

21724720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21724720 is an abundant number, since it is smaller than the sum of its proper divisors (28981856).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21724720 is a wasteful number, since it uses less digits than its factorization.

21724720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1069 (or 1063 counting only the distinct ones).

The product of its (nonzero) digits is 1568, while the sum is 25.

The square root of 21724720 is about 4660.9784380535. The cubic root of 21724720 is about 279.0303192001.

The spelling of 21724720 in words is "twenty-one million, seven hundred twenty-four thousand, seven hundred twenty".