21868909 has 2 divisors, whose sum is σ = 21868910. Its totient is φ = 21868908.

The previous prime is 21868849. The next prime is 21868921. The reversal of 21868909 is 90986812.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19053225 + 2815684 = 4365^2 + 1678^2 .

It is a cyclic number.

It is not a de Polignac number, because 21868909 - 2¹¹ = 21866861 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21868969) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10934454 + 10934455.

It is an arithmetic number, because the mean of its divisors is an integer number (10934455).

Almost surely, 2^21868909 is an apocalyptic number.

It is an amenable number.

21868909 is a deficient number, since it is larger than the sum of its proper divisors (1).

21868909 is an equidigital number, since it uses as much as digits as its factorization.

21868909 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 62208, while the sum is 43.

The square root of 21868909 is about 4676.4205328435. The cubic root of 21868909 is about 279.6462752656.

The spelling of 21868909 in words is "twenty-one million, eight hundred sixty-eight thousand, nine hundred nine".