21025909 has 2 divisors, whose sum is σ = 21025910. Its totient is φ = 21025908.

The previous prime is 21025897. The next prime is 21025937. The reversal of 21025909 is 90952012.

It is an a-pointer prime, because the next prime (21025937) can be obtained adding 21025909 to its sum of digits (28).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20566225 + 459684 = 4535^2 + 678^2 .

It is a cyclic number.

It is not a de Polignac number, because 21025909 - 2⁹ = 21025397 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21022909) 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, 10512954 + 10512955.

It is an arithmetic number, because the mean of its divisors is an integer number (10512955).

Almost surely, 2^21025909 is an apocalyptic number.

It is an amenable number.

21025909 is a deficient number, since it is larger than the sum of its proper divisors (1).

21025909 is an equidigital number, since it uses as much as digits as its factorization.

21025909 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1620, while the sum is 28.

The square root of 21025909 is about 4585.4017272209. The cubic root of 21025909 is about 276.0058328600.

The spelling of 21025909 in words is "twenty-one million, twenty-five thousand, nine hundred nine".