21389391 has 6 divisors (see below), whose sum is σ = 30895800. Its totient is φ = 14259588.

The previous prime is 21389377. The next prime is 21389393. The reversal of 21389391 is 19398312.

It is not a de Polignac number, because 21389391 - 2⁵ = 21389359 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21389393) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1188291 + ... + 1188308.

It is an arithmetic number, because the mean of its divisors is an integer number (5149300).

Almost surely, 2^21389391 is an apocalyptic number.

21389391 is a deficient number, since it is larger than the sum of its proper divisors (9506409).

21389391 is a wasteful number, since it uses less digits than its factorization.

21389391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2376605 (or 2376602 counting only the distinct ones).

The product of its digits is 11664, while the sum is 36.

The square root of 21389391 is about 4624.8665926705. The cubic root of 21389391 is about 277.5872236159.

The spelling of 21389391 in words is "twenty-one million, three hundred eighty-nine thousand, three hundred ninety-one".