21391241 has 4 divisors (see below), whose sum is σ = 22128900. Its totient is φ = 20653584.

The previous prime is 21391213. The next prime is 21391259. The reversal of 21391241 is 14219312.

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 16032016 + 5359225 = 4004^2 + 2315^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21391241 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 3 ways as a sum of consecutive naturals, for example, 368786 + ... + 368843.

It is an arithmetic number, because the mean of its divisors is an integer number (5532225).

Almost surely, 2^21391241 is an apocalyptic number.

It is an amenable number.

21391241 is a deficient number, since it is larger than the sum of its proper divisors (737659).

21391241 is an equidigital number, since it uses as much as digits as its factorization.

21391241 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 737658.

The product of its digits is 432, while the sum is 23.

The square root of 21391241 is about 4625.0665941152. The cubic root of 21391241 is about 277.5952263614.

The spelling of 21391241 in words is "twenty-one million, three hundred ninety-one thousand, two hundred forty-one".