21239605 has 8 divisors (see below), whose sum is σ = 25750872. Its totient is φ = 16816128.

The previous prime is 21239597. The next prime is 21239609. The reversal of 21239605 is 50693212.

It can be written as a sum of positive squares in 4 ways, for example, as 6355441 + 14884164 = 2521^2 + 3858^2 .

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 21239605 - 2³ = 21239597 is a prime.

It is a super-2 number, since 2×21239605² = 902241641112050, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21239609) 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 7 ways as a sum of consecutive naturals, for example, 21412 + ... + 22381.

It is an arithmetic number, because the mean of its divisors is an integer number (3218859).

Almost surely, 2^21239605 is an apocalyptic number.

It is an amenable number.

21239605 is a deficient number, since it is larger than the sum of its proper divisors (4511267).

21239605 is an equidigital number, since it uses as much as digits as its factorization.

21239605 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 43895.

The product of its (nonzero) digits is 3240, while the sum is 28.

The square root of 21239605 is about 4608.6445946721. The cubic root of 21239605 is about 276.9377409633.

The spelling of 21239605 in words is "twenty-one million, two hundred thirty-nine thousand, six hundred five".