21609389 has 2 divisors, whose sum is σ = 21609390. Its totient is φ = 21609388.

The previous prime is 21609377. The next prime is 21609391. The reversal of 21609389 is 98390612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16240900 + 5368489 = 4030^2 + 2317^2 .

It is a cyclic number.

It is not a de Polignac number, because 21609389 - 2⁴ = 21609373 is a prime.

It is a Sophie Germain prime.

Together with 21609391, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21609589) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10804694 + 10804695.

It is an arithmetic number, because the mean of its divisors is an integer number (10804695).

Almost surely, 2^21609389 is an apocalyptic number.

It is an amenable number.

21609389 is a deficient number, since it is larger than the sum of its proper divisors (1).

21609389 is an equidigital number, since it uses as much as digits as its factorization.

21609389 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 23328, while the sum is 38.

The square root of 21609389 is about 4648.5900012800. The cubic root of 21609389 is about 278.5356759100.

The spelling of 21609389 in words is "twenty-one million, six hundred nine thousand, three hundred eighty-nine".