21391291 has 8 divisors (see below), whose sum is σ = 22299920. Its totient is φ = 20500128.

The previous prime is 21391267. The next prime is 21391301. The reversal of 21391291 is 19219312.

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 21391291 - 2⁵ = 21391259 is a prime.

It is a Duffinian number.

It is a plaindrome in base 16.

It is not an unprimeable number, because it can be changed into a prime (21391211) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1836 + ... + 6793.

It is an arithmetic number, because the mean of its divisors is an integer number (2787490).

Almost surely, 2^21391291 is an apocalyptic number.

21391291 is a deficient number, since it is larger than the sum of its proper divisors (908629).

21391291 is an equidigital number, since it uses as much as digits as its factorization.

21391291 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8733.

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

The square root of 21391291 is about 4625.0719994396. The cubic root of 21391291 is about 277.5954426454.

The spelling of 21391291 in words is "twenty-one million, three hundred ninety-one thousand, two hundred ninety-one".