21027709 has 2 divisors, whose sum is σ = 21027710. Its totient is φ = 21027708.

The previous prime is 21027701. The next prime is 21027767. The reversal of 21027709 is 90772012.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12888100 + 8139609 = 3590^2 + 2853^2 .

It is a cyclic number.

It is not a de Polignac number, because 21027709 - 2³ = 21027701 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21027701) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10513854 + 10513855.

It is an arithmetic number, because the mean of its divisors is an integer number (10513855).

Almost surely, 2^21027709 is an apocalyptic number.

It is an amenable number.

21027709 is a deficient number, since it is larger than the sum of its proper divisors (1).

21027709 is an equidigital number, since it uses as much as digits as its factorization.

21027709 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1764, while the sum is 28.

The square root of 21027709 is about 4585.5979980805. The cubic root of 21027709 is about 276.0137087989.

It can be divided in two parts, 21027 and 709, that added together give a triangular number (21736 = T₂₀₈).

The spelling of 21027709 in words is "twenty-one million, twenty-seven thousand, seven hundred nine".