21857609 has 2 divisors, whose sum is σ = 21857610. Its totient is φ = 21857608.

The previous prime is 21857579. The next prime is 21857617. The reversal of 21857609 is 90675812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15840400 + 6017209 = 3980^2 + 2453^2 .

It is a cyclic number.

It is not a de Polignac number, because 21857609 - 2¹⁶ = 21792073 is a prime.

It is not a weakly prime, because it can be changed into another prime (21857669) 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, 10928804 + 10928805.

It is an arithmetic number, because the mean of its divisors is an integer number (10928805).

Almost surely, 2^21857609 is an apocalyptic number.

It is an amenable number.

21857609 is a deficient number, since it is larger than the sum of its proper divisors (1).

21857609 is an equidigital number, since it uses as much as digits as its factorization.

21857609 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 30240, while the sum is 38.

The square root of 21857609 is about 4675.2121876980. The cubic root of 21857609 is about 279.5981011303.

The spelling of 21857609 in words is "twenty-one million, eight hundred fifty-seven thousand, six hundred nine".