21811387 has 8 divisors (see below), whose sum is σ = 23536800. Its totient is φ = 20092800.

The previous prime is 21811367. The next prime is 21811397. The reversal of 21811387 is 78311812.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a de Polignac number, because none of the positive numbers 2^k-21811387 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21811367) 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 7 ways as a sum of consecutive naturals, for example, 6387 + ... + 9187.

It is an arithmetic number, because the mean of its divisors is an integer number (2942100).

Almost surely, 2^21811387 is an apocalyptic number.

21811387 is a deficient number, since it is larger than the sum of its proper divisors (1725413).

21811387 is a wasteful number, since it uses less digits than its factorization.

21811387 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3413.

The product of its digits is 2688, while the sum is 31.

The square root of 21811387 is about 4670.2662664992. The cubic root of 21811387 is about 279.4008745577.

The spelling of 21811387 in words is "twenty-one million, eight hundred eleven thousand, three hundred eighty-seven".