21239717 has 2 divisors, whose sum is σ = 21239718. Its totient is φ = 21239716.

The previous prime is 21239711. The next prime is 21239731. The reversal of 21239717 is 71793212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16248961 + 4990756 = 4031^2 + 2234^2 .

It is a cyclic number.

It is not a de Polignac number, because 21239717 - 2⁸ = 21239461 is a prime.

It is a super-2 number, since 2×21239717² = 902251156480178, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21239711) 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 as a sum of consecutive naturals, namely, 10619858 + 10619859.

It is an arithmetic number, because the mean of its divisors is an integer number (10619859).

Almost surely, 2^21239717 is an apocalyptic number.

It is an amenable number.

21239717 is a deficient number, since it is larger than the sum of its proper divisors (1).

21239717 is an equidigital number, since it uses as much as digits as its factorization.

21239717 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5292, while the sum is 32.

The square root of 21239717 is about 4608.6567457341. The cubic root of 21239717 is about 276.9382277422.

The spelling of 21239717 in words is "twenty-one million, two hundred thirty-nine thousand, seven hundred seventeen".