21217839 has 4 divisors (see below), whose sum is σ = 28290456. Its totient is φ = 14145224.

The previous prime is 21217837. The next prime is 21217849. The reversal of 21217839 is 93871212.

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

It is a cyclic number.

It is not a de Polignac number, because 21217839 - 2¹ = 21217837 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21217837) 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, 3536304 + ... + 3536309.

It is an arithmetic number, because the mean of its divisors is an integer number (7072614).

Almost surely, 2^21217839 is an apocalyptic number.

21217839 is a deficient number, since it is larger than the sum of its proper divisors (7072617).

21217839 is an equidigital number, since it uses as much as digits as its factorization.

21217839 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7072616.

The product of its digits is 6048, while the sum is 33.

The square root of 21217839 is about 4606.2825575512. The cubic root of 21217839 is about 276.8431082067.

The spelling of 21217839 in words is "twenty-one million, two hundred seventeen thousand, eight hundred thirty-nine".