21989920 has 24 divisors (see below), whose sum is σ = 51951564. Its totient is φ = 8795904.

The previous prime is 21989911. The next prime is 21989941. The reversal of 21989920 is 2998912.

It can be written as a sum of positive squares in 2 ways, for example, as 21418384 + 571536 = 4628^2 + 756^2 .

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors.

It is a Harshad number since it is a multiple of its sum of digits (40).

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 68559 + ... + 68878.

Almost surely, 2^21989920 is an apocalyptic number.

21989920 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21989920 is an abundant number, since it is smaller than the sum of its proper divisors (29961644).

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

21989920 is a wasteful number, since it uses less digits than its factorization.

21989920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 137452 (or 137444 counting only the distinct ones).

The product of its (nonzero) digits is 23328, while the sum is 40.

The square root of 21989920 is about 4689.3411051021. The cubic root of 21989920 is about 280.1611317454.

The spelling of 21989920 in words is "twenty-one million, nine hundred eighty-nine thousand, nine hundred twenty".