21724780 has 48 divisors (see below), whose sum is σ = 56883456. Its totient is φ = 6770880.

The previous prime is 21724757. The next prime is 21724783. The reversal of 21724780 is 8742712.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21724783) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5514 + ... + 8593.

It is an arithmetic number, because the mean of its divisors is an integer number (1185072).

Almost surely, 2^21724780 is an apocalyptic number.

21724780 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21724780 is an abundant number, since it is smaller than the sum of its proper divisors (35158676).

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

21724780 is a wasteful number, since it uses less digits than its factorization.

21724780 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14134 (or 14132 counting only the distinct ones).

The product of its (nonzero) digits is 6272, while the sum is 31.

The square root of 21724780 is about 4660.9848744659. The cubic root of 21724780 is about 279.0305760780.

The spelling of 21724780 in words is "twenty-one million, seven hundred twenty-four thousand, seven hundred eighty".