21957990 has 16 divisors (see below), whose sum is σ = 52699248. Its totient is φ = 5855456.

The previous prime is 21957989. The next prime is 21957997. The reversal of 21957990 is 9975912.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21957997) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 365937 + ... + 365996.

It is an arithmetic number, because the mean of its divisors is an integer number (3293703).

Almost surely, 2^21957990 is an apocalyptic number.

21957990 is an abundant number, since it is smaller than the sum of its proper divisors (30741258).

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

21957990 is a wasteful number, since it uses less digits than its factorization.

21957990 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 731943.

The product of its (nonzero) digits is 51030, while the sum is 42.

The square root of 21957990 is about 4685.9353388625. The cubic root of 21957990 is about 280.0254653710.

The spelling of 21957990 in words is "twenty-one million, nine hundred fifty-seven thousand, nine hundred ninety".