21988399 has 4 divisors (see below), whose sum is σ = 22161664. Its totient is φ = 21815136.

The previous prime is 21988387. The next prime is 21988411. The reversal of 21988399 is 99388912.

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

It is an interprime number because it is at equal distance from previous prime (21988387) and next prime (21988411).

It is a cyclic number.

It is not a de Polignac number, because 21988399 - 2⁵ = 21988367 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21988319) 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 3 ways as a sum of consecutive naturals, for example, 86442 + ... + 86695.

It is an arithmetic number, because the mean of its divisors is an integer number (5540416).

Almost surely, 2^21988399 is an apocalyptic number.

21988399 is a deficient number, since it is larger than the sum of its proper divisors (173265).

21988399 is a wasteful number, since it uses less digits than its factorization.

21988399 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 173264.

The product of its digits is 279936, while the sum is 49.

The square root of 21988399 is about 4689.1789259955. The cubic root of 21988399 is about 280.1546721963.

The spelling of 21988399 in words is "twenty-one million, nine hundred eighty-eight thousand, three hundred ninety-nine".