21147999 has 4 divisors (see below), whose sum is σ = 28197336. Its totient is φ = 14098664.

The previous prime is 21147967. The next prime is 21148013. The reversal of 21147999 is 99974112.

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 21147999 - 2⁵ = 21147967 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21147999.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21147499) 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, 3524664 + ... + 3524669.

It is an arithmetic number, because the mean of its divisors is an integer number (7049334).

Almost surely, 2^21147999 is an apocalyptic number.

21147999 is a deficient number, since it is larger than the sum of its proper divisors (7049337).

21147999 is an equidigital number, since it uses as much as digits as its factorization.

21147999 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7049336.

The product of its digits is 40824, while the sum is 42.

The square root of 21147999 is about 4598.6953584685. The cubic root of 21147999 is about 276.5390248452.

The spelling of 21147999 in words is "twenty-one million, one hundred forty-seven thousand, nine hundred ninety-nine".