21698321 has 2 divisors, whose sum is σ = 21698322. Its totient is φ = 21698320.

The previous prime is 21698311. The next prime is 21698387. The reversal of 21698321 is 12389612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20566225 + 1132096 = 4535^2 + 1064^2 .

It is a cyclic number.

It is not a de Polignac number, because 21698321 - 2²² = 17504017 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

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

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21698311) 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, 10849160 + 10849161.

It is an arithmetic number, because the mean of its divisors is an integer number (10849161).

Almost surely, 2^21698321 is an apocalyptic number.

It is an amenable number.

21698321 is a deficient number, since it is larger than the sum of its proper divisors (1).

21698321 is an equidigital number, since it uses as much as digits as its factorization.

21698321 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5184, while the sum is 32.

The square root of 21698321 is about 4658.1456610973. The cubic root of 21698321 is about 278.9172512743.

The spelling of 21698321 in words is "twenty-one million, six hundred ninety-eight thousand, three hundred twenty-one".