21921817 has 2 divisors, whose sum is σ = 21921818. Its totient is φ = 21921816.

The previous prime is 21921811. The next prime is 21921847. The reversal of 21921817 is 71812912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21752896 + 168921 = 4664^2 + 411^2 .

It is a cyclic number.

It is not a de Polignac number, because 21921817 - 2⁷ = 21921689 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21921811) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10960908 + 10960909.

It is an arithmetic number, because the mean of its divisors is an integer number (10960909).

Almost surely, 2^21921817 is an apocalyptic number.

It is an amenable number.

21921817 is a deficient number, since it is larger than the sum of its proper divisors (1).

21921817 is an equidigital number, since it uses as much as digits as its factorization.

21921817 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2016, while the sum is 31.

The square root of 21921817 is about 4682.0740062498. The cubic root of 21921817 is about 279.8716120579.

The spelling of 21921817 in words is "twenty-one million, nine hundred twenty-one thousand, eight hundred seventeen".