21757640 has 32 divisors (see below), whose sum is σ = 49351680. Its totient is φ = 8632512.

The previous prime is 21757633. The next prime is 21757643. The reversal of 21757640 is 4675712.

It is a junction number, because it is equal to n+sod(n) for n = 21757597 and 21757606.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21757643) 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, 2939 + ... + 7221.

It is an arithmetic number, because the mean of its divisors is an integer number (1542240).

Almost surely, 2^21757640 is an apocalyptic number.

21757640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21757640 is an abundant number, since it is smaller than the sum of its proper divisors (27594040).

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

21757640 is a wasteful number, since it uses less digits than its factorization.

21757640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4421 (or 4417 counting only the distinct ones).

The product of its (nonzero) digits is 11760, while the sum is 32.

The square root of 21757640 is about 4664.5085486040. The cubic root of 21757640 is about 279.1711885607.

The spelling of 21757640 in words is "twenty-one million, seven hundred fifty-seven thousand, six hundred forty".