21297509 has 2 divisors, whose sum is σ = 21297510. Its totient is φ = 21297508.

The previous prime is 21297487. The next prime is 21297539. The reversal of 21297509 is 90579212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15760900 + 5536609 = 3970^2 + 2353^2 .

It is a cyclic number.

It is not a de Polignac number, because 21297509 - 2²⁴ = 4520293 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21297539) 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, 10648754 + 10648755.

It is an arithmetic number, because the mean of its divisors is an integer number (10648755).

Almost surely, 2^21297509 is an apocalyptic number.

It is an amenable number.

21297509 is a deficient number, since it is larger than the sum of its proper divisors (1).

21297509 is an equidigital number, since it uses as much as digits as its factorization.

21297509 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 11340, while the sum is 35.

The square root of 21297509 is about 4614.9224262169. The cubic root of 21297509 is about 277.1891777260.

The spelling of 21297509 in words is "twenty-one million, two hundred ninety-seven thousand, five hundred nine".