21312399 has 4 divisors (see below), whose sum is σ = 28416536. Its totient is φ = 14208264.

The previous prime is 21312341. The next prime is 21312427. The reversal of 21312399 is 99321312.

It is a happy number.

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

It is not a de Polignac number, because 21312399 - 2¹² = 21308303 is a prime.

It is a super-2 number, since 2×21312399² = 908436702270402, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21312299) 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, 3552064 + ... + 3552069.

It is an arithmetic number, because the mean of its divisors is an integer number (7104134).

Almost surely, 2^21312399 is an apocalyptic number.

21312399 is a deficient number, since it is larger than the sum of its proper divisors (7104137).

21312399 is an equidigital number, since it uses as much as digits as its factorization.

21312399 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7104136.

The product of its digits is 2916, while the sum is 30.

The square root of 21312399 is about 4616.5353892286. The cubic root of 21312399 is about 277.2537609497.

The spelling of 21312399 in words is "twenty-one million, three hundred twelve thousand, three hundred ninety-nine".