21972399 has 4 divisors (see below), whose sum is σ = 29296536. Its totient is φ = 14648264.

The previous prime is 21972373. The next prime is 21972407. The reversal of 21972399 is 99327912.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21972399 - 2⁷ = 21972271 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21972399.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21972319) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3662064 + ... + 3662069.

It is an arithmetic number, because the mean of its divisors is an integer number (7324134).

Almost surely, 2^21972399 is an apocalyptic number.

21972399 is a deficient number, since it is larger than the sum of its proper divisors (7324137).

21972399 is an equidigital number, since it uses as much as digits as its factorization.

21972399 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7324136.

The product of its digits is 61236, while the sum is 42.

The square root of 21972399 is about 4687.4725599197. The cubic root of 21972399 is about 280.0867035911.

The spelling of 21972399 in words is "twenty-one million, nine hundred seventy-two thousand, three hundred ninety-nine".