21023309 has 2 divisors, whose sum is σ = 21023310. Its totient is φ = 21023308.

The previous prime is 21023287. The next prime is 21023323. The reversal of 21023309 is 90332012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20675209 + 348100 = 4547^2 + 590^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21023309 is a prime.

It is a Sophie Germain 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 (21023209) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10511654 + 10511655.

It is an arithmetic number, because the mean of its divisors is an integer number (10511655).

Almost surely, 2^21023309 is an apocalyptic number.

It is an amenable number.

21023309 is a deficient number, since it is larger than the sum of its proper divisors (1).

21023309 is an equidigital number, since it uses as much as digits as its factorization.

21023309 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 324, while the sum is 20.

The square root of 21023309 is about 4585.1182100356. The cubic root of 21023309 is about 275.9944557102.

The spelling of 21023309 in words is "twenty-one million, twenty-three thousand, three hundred nine".