21720000 has 140 divisors (see below), whose sum is σ = 72208136. Its totient is φ = 5760000.

The previous prime is 21719989. The next prime is 21720007. The reversal of 21720000 is 2712.

It is a Harshad number since it is a multiple of its sum of digits (12).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21720007) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 119910 + ... + 120090.

Almost surely, 2^21720000 is an apocalyptic number.

21720000 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21720000, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36104068).

21720000 is an abundant number, since it is smaller than the sum of its proper divisors (50488136).

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

21720000 is an equidigital number, since it uses as much as digits as its factorization.

21720000 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 216 (or 191 counting only the distinct ones).

The product of its (nonzero) digits is 28, while the sum is 12.

The square root of 21720000 is about 4660.4720790924. The cubic root of 21720000 is about 279.0101099868.

Adding to 21720000 its reverse (2712), we get a palindrome (21722712).

The spelling of 21720000 in words is "twenty-one million, seven hundred twenty thousand".