21005597 has 2 divisors, whose sum is σ = 21005598. Its totient is φ = 21005596.

The previous prime is 21005561. The next prime is 21005609. The reversal of 21005597 is 79550012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20894041 + 111556 = 4571^2 + 334^2 .

It is a cyclic number.

It is not a de Polignac number, because 21005597 - 2¹⁶ = 20940061 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21005297) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10502798 + 10502799.

It is an arithmetic number, because the mean of its divisors is an integer number (10502799).

Almost surely, 2^21005597 is an apocalyptic number.

It is an amenable number.

21005597 is a deficient number, since it is larger than the sum of its proper divisors (1).

21005597 is an equidigital number, since it uses as much as digits as its factorization.

21005597 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3150, while the sum is 29.

The square root of 21005597 is about 4583.1863370367. The cubic root of 21005597 is about 275.9169260936.

The spelling of 21005597 in words is "twenty-one million, five thousand, five hundred ninety-seven".