21166387 has 4 divisors (see below), whose sum is σ = 23090616. Its totient is φ = 19242160.

The previous prime is 21166381. The next prime is 21166441. The reversal of 21166387 is 78366112.

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 21166387 - 2¹⁹ = 20642099 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21166381) 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, 962098 + ... + 962119.

It is an arithmetic number, because the mean of its divisors is an integer number (5772654).

Almost surely, 2^21166387 is an apocalyptic number.

21166387 is a deficient number, since it is larger than the sum of its proper divisors (1924229).

21166387 is a wasteful number, since it uses less digits than its factorization.

21166387 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1924228.

The product of its digits is 12096, while the sum is 34.

The square root of 21166387 is about 4600.6941867505. The cubic root of 21166387 is about 276.6191510471.

The spelling of 21166387 in words is "twenty-one million, one hundred sixty-six thousand, three hundred eighty-seven".