21729517 has 2 divisors, whose sum is σ = 21729518. Its totient is φ = 21729516.

The previous prime is 21729511. The next prime is 21729527. The reversal of 21729517 is 71592712.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16434916 + 5294601 = 4054^2 + 2301^2 .

It is a cyclic number.

It is not a de Polignac number, because 21729517 - 2³ = 21729509 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21729511) 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 as a sum of consecutive naturals, namely, 10864758 + 10864759.

It is an arithmetic number, because the mean of its divisors is an integer number (10864759).

Almost surely, 2^21729517 is an apocalyptic number.

It is an amenable number.

21729517 is a deficient number, since it is larger than the sum of its proper divisors (1).

21729517 is an equidigital number, since it uses as much as digits as its factorization.

21729517 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 8820, while the sum is 34.

The square root of 21729517 is about 4661.4930011746. The cubic root of 21729517 is about 279.0508550986.

The spelling of 21729517 in words is "twenty-one million, seven hundred twenty-nine thousand, five hundred seventeen".