21004309 has 2 divisors, whose sum is σ = 21004310. Its totient is φ = 21004308.

The previous prime is 21004303. The next prime is 21004331. The reversal of 21004309 is 90340012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20958084 + 46225 = 4578^2 + 215^2 .

It is a cyclic number.

It is not a de Polignac number, because 21004309 - 2³ = 21004301 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21004301) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10502154 + 10502155.

It is an arithmetic number, because the mean of its divisors is an integer number (10502155).

Almost surely, 2^21004309 is an apocalyptic number.

It is an amenable number.

21004309 is a deficient number, since it is larger than the sum of its proper divisors (1).

21004309 is an equidigital number, since it uses as much as digits as its factorization.

21004309 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 216, while the sum is 19.

The square root of 21004309 is about 4583.0458212852. The cubic root of 21004309 is about 275.9112865131.

The spelling of 21004309 in words is "twenty-one million, four thousand, three hundred nine".