21721920 has 224 divisors, whose sum is σ = 80320896. Its totient is φ = 4956160.

The previous prime is 21721907. The next prime is 21721927. The reversal of 21721920 is 2912712.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a Saint-Exupery number, since it is equal to the product of the sides of a Pythagorean triangle: 374 × 330 × 176.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21721927) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 1277752 + ... + 1277768.

Almost surely, 2^21721920 is an apocalyptic number.

21721920 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 21721920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (40160448).

21721920 is an abundant number, since it is smaller than the sum of its proper divisors (58598976).

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

21721920 is a wasteful number, since it uses less digits than its factorization.

21721920 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 70 (or 38 counting only the distinct ones).

The product of its (nonzero) digits is 504, while the sum is 24.

The square root of 21721920 is about 4660.6780622566. The cubic root of 21721920 is about 279.0183310369.

The spelling of 21721920 in words is "twenty-one million, seven hundred twenty-one thousand, nine hundred twenty".