21099972 has 24 divisors (see below), whose sum is σ = 49696416. Its totient is φ = 6967168.

The previous prime is 21099959. The next prime is 21099973. The reversal of 21099972 is 27999012.

It is a happy number.

It is a self number, because there is not a number n which added to its sum of digits gives 21099972.

It is not an unprimeable number, because it can be changed into a prime (21099973) 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, 6933 + ... + 9500.

It is an arithmetic number, because the mean of its divisors is an integer number (2070684).

Almost surely, 2^21099972 is an apocalyptic number.

It is an amenable number.

21099972 is an abundant number, since it is smaller than the sum of its proper divisors (28596444).

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

21099972 is a wasteful number, since it uses less digits than its factorization.

21099972 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16547 (or 16545 counting only the distinct ones).

The product of its (nonzero) digits is 20412, while the sum is 39.

The square root of 21099972 is about 4593.4705833389. The cubic root of 21099972 is about 276.3295265943.

The spelling of 21099972 in words is "twenty-one million, ninety-nine thousand, nine hundred seventy-two".