21399351 has 4 divisors (see below), whose sum is σ = 28532472. Its totient is φ = 14266232.

The previous prime is 21399319. The next prime is 21399353. The reversal of 21399351 is 15399312.

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 21399351 - 2⁵ = 21399319 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21399353) 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, 3566556 + ... + 3566561.

It is an arithmetic number, because the mean of its divisors is an integer number (7133118).

Almost surely, 2^21399351 is an apocalyptic number.

21399351 is a deficient number, since it is larger than the sum of its proper divisors (7133121).

21399351 is an equidigital number, since it uses as much as digits as its factorization.

21399351 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7133120.

The product of its digits is 7290, while the sum is 33.

The square root of 21399351 is about 4625.9432551643. The cubic root of 21399351 is about 277.6303032236.

The spelling of 21399351 in words is "twenty-one million, three hundred ninety-nine thousand, three hundred fifty-one".