21868709 has 2 divisors, whose sum is σ = 21868710. Its totient is φ = 21868708.

The previous prime is 21868669. The next prime is 21868723. The reversal of 21868709 is 90786812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16564900 + 5303809 = 4070^2 + 2303^2 .

It is a cyclic number.

It is not a de Polignac number, because 21868709 - 2¹² = 21864613 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 (21868789) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10934354 + 10934355.

It is an arithmetic number, because the mean of its divisors is an integer number (10934355).

Almost surely, 2^21868709 is an apocalyptic number.

It is an amenable number.

21868709 is a deficient number, since it is larger than the sum of its proper divisors (1).

21868709 is an equidigital number, since it uses as much as digits as its factorization.

21868709 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 48384, while the sum is 41.

The square root of 21868709 is about 4676.3991489179. The cubic root of 21868709 is about 279.6454227703.

The spelling of 21868709 in words is "twenty-one million, eight hundred sixty-eight thousand, seven hundred nine".