21916399 has 4 divisors (see below), whose sum is σ = 22180536. Its totient is φ = 21652264.

The previous prime is 21916397. The next prime is 21916439. The reversal of 21916399 is 99361912.

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 21916399 - 2¹ = 21916397 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 (21916393) 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, 131944 + ... + 132109.

It is an arithmetic number, because the mean of its divisors is an integer number (5545134).

Almost surely, 2^21916399 is an apocalyptic number.

21916399 is a deficient number, since it is larger than the sum of its proper divisors (264137).

21916399 is an equidigital number, since it uses as much as digits as its factorization.

21916399 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 264136.

The product of its digits is 26244, while the sum is 40.

The square root of 21916399 is about 4681.4953807518. The cubic root of 21916399 is about 279.8485533042.

The spelling of 21916399 in words is "twenty-one million, nine hundred sixteen thousand, three hundred ninety-nine".