21188161 has 4 divisors (see below), whose sum is σ = 21760852. Its totient is φ = 20615472.

The previous prime is 21188149. The next prime is 21188179. The reversal of 21188161 is 16188112.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 16483600 + 4704561 = 4060^2 + 2169^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21188161 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21188261) 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, 286290 + ... + 286363.

It is an arithmetic number, because the mean of its divisors is an integer number (5440213).

Almost surely, 2^21188161 is an apocalyptic number.

It is an amenable number.

21188161 is a deficient number, since it is larger than the sum of its proper divisors (572691).

21188161 is an equidigital number, since it uses as much as digits as its factorization.

21188161 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 572690.

The product of its digits is 768, while the sum is 28.

The square root of 21188161 is about 4603.0599605045. The cubic root of 21188161 is about 276.7139718470.

The spelling of 21188161 in words is "twenty-one million, one hundred eighty-eight thousand, one hundred sixty-one".