21670309 has 2 divisors, whose sum is σ = 21670310. Its totient is φ = 21670308.

The previous prime is 21670307. The next prime is 21670321. The reversal of 21670309 is 90307612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14364100 + 7306209 = 3790^2 + 2703^2 .

It is a cyclic number.

It is not a de Polignac number, because 21670309 - 2¹ = 21670307 is a prime.

Together with 21670307, it forms a pair of twin primes.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21670303) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10835154 + 10835155.

It is an arithmetic number, because the mean of its divisors is an integer number (10835155).

Almost surely, 2^21670309 is an apocalyptic number.

It is an amenable number.

21670309 is a deficient number, since it is larger than the sum of its proper divisors (1).

21670309 is an equidigital number, since it uses as much as digits as its factorization.

21670309 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2268, while the sum is 28.

The square root of 21670309 is about 4655.1379141761. The cubic root of 21670309 is about 278.7971744782.

The spelling of 21670309 in words is "twenty-one million, six hundred seventy thousand, three hundred nine".