21275809 has 2 divisors, whose sum is σ = 21275810. Its totient is φ = 21275808.

The previous prime is 21275747. The next prime is 21275831. The reversal of 21275809 is 90857212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15776784 + 5499025 = 3972^2 + 2345^2 .

It is a cyclic number.

It is not a de Polignac number, because 21275809 - 2⁹ = 21275297 is a prime.

It is a super-4 number, since 4×21275809⁴ (a number of 30 digits) contains 4444 as substring.

It is not a weakly prime, because it can be changed into another prime (21275869) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10637904 + 10637905.

It is an arithmetic number, because the mean of its divisors is an integer number (10637905).

Almost surely, 2^21275809 is an apocalyptic number.

It is an amenable number.

21275809 is a deficient number, since it is larger than the sum of its proper divisors (1).

21275809 is an equidigital number, since it uses as much as digits as its factorization.

21275809 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 10080, while the sum is 34.

The square root of 21275809 is about 4612.5707582649. The cubic root of 21275809 is about 277.0950031881.

The spelling of 21275809 in words is "twenty-one million, two hundred seventy-five thousand, eight hundred nine".