21166891 has 2 divisors, whose sum is σ = 21166892. Its totient is φ = 21166890.

The previous prime is 21166883. The next prime is 21166903. The reversal of 21166891 is 19866112.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21166891 - 2³ = 21166883 is a prime.

It is not a weakly prime, because it can be changed into another prime (21166991) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10583445 + 10583446.

It is an arithmetic number, because the mean of its divisors is an integer number (10583446).

Almost surely, 2^21166891 is an apocalyptic number.

21166891 is a deficient number, since it is larger than the sum of its proper divisors (1).

21166891 is an equidigital number, since it uses as much as digits as its factorization.

21166891 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5184, while the sum is 34.

The square root of 21166891 is about 4600.7489607671. The cubic root of 21166891 is about 276.6213465871.

The spelling of 21166891 in words is "twenty-one million, one hundred sixty-six thousand, eight hundred ninety-one".