21139221 has 4 divisors (see below), whose sum is σ = 28185632. Its totient is φ = 14092812.

The previous prime is 21139213. The next prime is 21139243. The reversal of 21139221 is 12293112.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 21139221 - 2³ = 21139213 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21139201) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3523201 + ... + 3523206.

It is an arithmetic number, because the mean of its divisors is an integer number (7046408).

Almost surely, 2^21139221 is an apocalyptic number.

It is an amenable number.

21139221 is a deficient number, since it is larger than the sum of its proper divisors (7046411).

21139221 is an equidigital number, since it uses as much as digits as its factorization.

21139221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7046410.

The product of its digits is 216, while the sum is 21.

The square root of 21139221 is about 4597.7408582912. The cubic root of 21139221 is about 276.5007580964.

The spelling of 21139221 in words is "twenty-one million, one hundred thirty-nine thousand, two hundred twenty-one".