21757440 has 80 divisors (see below), whose sum is σ = 69580368. Its totient is φ = 5799936.

The previous prime is 21757423. The next prime is 21757447. The reversal of 21757440 is 4475712.

It is a tau number, because it is divible by the number of its divisors (80).

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a junction number, because it is equal to n+sod(n) for n = 21757398 and 21757407.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21757447) 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, 6264 + ... + 9096.

Almost surely, 2^21757440 is an apocalyptic number.

21757440 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 21757440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34790184).

21757440 is an abundant number, since it is smaller than the sum of its proper divisors (47822928).

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

21757440 is an equidigital number, since it uses as much as digits as its factorization.

21757440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2859 (or 2843 counting only the distinct ones).

The product of its (nonzero) digits is 7840, while the sum is 30.

The square root of 21757440 is about 4664.4871100690. The cubic root of 21757440 is about 279.1703331614.

The spelling of 21757440 in words is "twenty-one million, seven hundred fifty-seven thousand, four hundred forty".