21388771 has 4 divisors (see below), whose sum is σ = 22646952. Its totient is φ = 20130592.

The previous prime is 21388769. The next prime is 21388777. The reversal of 21388771 is 17788312.

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 21388771 - 2¹ = 21388769 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21388771.

It is not an unprimeable number, because it can be changed into a prime (21388777) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 629065 + ... + 629098.

It is an arithmetic number, because the mean of its divisors is an integer number (5661738).

Almost surely, 2^21388771 is an apocalyptic number.

21388771 is a deficient number, since it is larger than the sum of its proper divisors (1258181).

21388771 is a wasteful number, since it uses less digits than its factorization.

21388771 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1258180.

The product of its digits is 18816, while the sum is 37.

The square root of 21388771 is about 4624.7995632243. The cubic root of 21388771 is about 277.5845415114.

The spelling of 21388771 in words is "twenty-one million, three hundred eighty-eight thousand, seven hundred seventy-one".