21231191 has 4 divisors (see below), whose sum is σ = 21241632. Its totient is φ = 21220752.

The previous prime is 21231173. The next prime is 21231241. The reversal of 21231191 is 19113212.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21231191 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21231391) 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, 1070 + ... + 6603.

It is an arithmetic number, because the mean of its divisors is an integer number (5310408).

Almost surely, 2^21231191 is an apocalyptic number.

21231191 is a deficient number, since it is larger than the sum of its proper divisors (10441).

21231191 is an equidigital number, since it uses as much as digits as its factorization.

21231191 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10440.

The product of its digits is 108, while the sum is 20.

The square root of 21231191 is about 4607.7316545129. The cubic root of 21231191 is about 276.9011668068.

The spelling of 21231191 in words is "twenty-one million, two hundred thirty-one thousand, one hundred ninety-one".