21201391 has 4 divisors (see below), whose sum is σ = 21224592. Its totient is φ = 21178192.

The previous prime is 21201379. The next prime is 21201419. The reversal of 21201391 is 19310212.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21201391 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 (21201311) 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 3 ways as a sum of consecutive naturals, for example, 10171 + ... + 12076.

It is an arithmetic number, because the mean of its divisors is an integer number (5306148).

Almost surely, 2^21201391 is an apocalyptic number.

21201391 is a deficient number, since it is larger than the sum of its proper divisors (23201).

21201391 is an equidigital number, since it uses as much as digits as its factorization.

21201391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23200.

The product of its (nonzero) digits is 108, while the sum is 19.

The square root of 21201391 is about 4604.4968237583. The cubic root of 21201391 is about 276.7715537539.

The spelling of 21201391 in words is "twenty-one million, two hundred one thousand, three hundred ninety-one".