21694921 has 2 divisors, whose sum is σ = 21694922. Its totient is φ = 21694920.

The previous prime is 21694891. The next prime is 21694927. The reversal of 21694921 is 12949612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16289296 + 5405625 = 4036^2 + 2325^2 .

It is a cyclic number.

It is not a de Polignac number, because 21694921 - 2⁵ = 21694889 is a prime.

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

It is not a weakly prime, because it can be changed into another prime (21694927) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10847460 + 10847461.

It is an arithmetic number, because the mean of its divisors is an integer number (10847461).

Almost surely, 2^21694921 is an apocalyptic number.

It is an amenable number.

21694921 is a deficient number, since it is larger than the sum of its proper divisors (1).

21694921 is an equidigital number, since it uses as much as digits as its factorization.

21694921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 7776, while the sum is 34.

The square root of 21694921 is about 4657.7806947086. The cubic root of 21694921 is about 278.9026822793.

The spelling of 21694921 in words is "twenty-one million, six hundred ninety-four thousand, nine hundred twenty-one".