21388791 has 16 divisors (see below), whose sum is σ = 29754368. Its totient is φ = 13651200.

The previous prime is 21388789. The next prime is 21388799. The reversal of 21388791 is 19788312.

It is not a de Polignac number, because 21388791 - 2¹ = 21388789 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 (21388799) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7836 + ... + 10206.

It is an arithmetic number, because the mean of its divisors is an integer number (1859648).

Almost surely, 2^21388791 is an apocalyptic number.

21388791 is a deficient number, since it is larger than the sum of its proper divisors (8365577).

21388791 is a wasteful number, since it uses less digits than its factorization.

21388791 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2502.

The product of its digits is 24192, while the sum is 39.

The square root of 21388791 is about 4624.8017254797. The cubic root of 21388791 is about 277.5846280317.

The spelling of 21388791 in words is "twenty-one million, three hundred eighty-eight thousand, seven hundred ninety-one".