21579709 has 2 divisors, whose sum is σ = 21579710. Its totient is φ = 21579708.

The previous prime is 21579707. The next prime is 21579731. The reversal of 21579709 is 90797512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16426809 + 5152900 = 4053^2 + 2270^2 .

It is a cyclic number.

It is not a de Polignac number, because 21579709 - 2¹ = 21579707 is a prime.

Together with 21579707, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21579707) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10789854 + 10789855.

It is an arithmetic number, because the mean of its divisors is an integer number (10789855).

Almost surely, 2^21579709 is an apocalyptic number.

It is an amenable number.

21579709 is a deficient number, since it is larger than the sum of its proper divisors (1).

21579709 is an equidigital number, since it uses as much as digits as its factorization.

21579709 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 39690, while the sum is 40.

The square root of 21579709 is about 4645.3965385099. The cubic root of 21579709 is about 278.4080966964.

The spelling of 21579709 in words is "twenty-one million, five hundred seventy-nine thousand, seven hundred nine".