21931291 has 8 divisors (see below), whose sum is σ = 22896000. Its totient is φ = 20982720.

The previous prime is 21931289. The next prime is 21931297. The reversal of 21931291 is 19213912.

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

It is a cyclic number.

It is not a de Polignac number, because 21931291 - 2¹ = 21931289 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21931297) 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, 1216 + ... + 6733.

It is an arithmetic number, because the mean of its divisors is an integer number (2862000).

Almost surely, 2^21931291 is an apocalyptic number.

21931291 is a deficient number, since it is larger than the sum of its proper divisors (964709).

21931291 is an equidigital number, since it uses as much as digits as its factorization.

21931291 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8069.

The product of its digits is 972, while the sum is 28.

The square root of 21931291 is about 4683.0856280875. The cubic root of 21931291 is about 279.9119238285.

It can be divided in two parts, 21931 and 291, that added together give a palindrome (22222).

The spelling of 21931291 in words is "twenty-one million, nine hundred thirty-one thousand, two hundred ninety-one".