21957840 has 60 divisors (see below), whose sum is σ = 73744164. Its totient is φ = 5855232.

The previous prime is 21957811. The next prime is 21957841. The reversal of 21957840 is 4875912.

It can be written as a sum of positive squares in 2 ways, for example, as 12446784 + 9511056 = 3528^2 + 3084^2 .

It is a tau number, because it is divible by the number of its divisors (60).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 21957795 and 21957804.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21957841) 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 11 ways as a sum of consecutive naturals, for example, 14529 + ... + 15968.

Almost surely, 2^21957840 is an apocalyptic number.

21957840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21957840 is an abundant number, since it is smaller than the sum of its proper divisors (51786324).

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

21957840 is a wasteful number, since it uses less digits than its factorization.

21957840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 30516 (or 30507 counting only the distinct ones).

The product of its (nonzero) digits is 20160, while the sum is 36.

The square root of 21957840 is about 4685.9193334926. The cubic root of 21957840 is about 280.0248277304.

The spelling of 21957840 in words is "twenty-one million, nine hundred fifty-seven thousand, eight hundred forty".