21921017 has 2 divisors, whose sum is σ = 21921018. Its totient is φ = 21921016.

The previous prime is 21920989. The next prime is 21921059. The reversal of 21921017 is 71012912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21196816 + 724201 = 4604^2 + 851^2 .

It is a cyclic number.

It is not a de Polignac number, because 21921017 - 2¹⁸ = 21658873 is a prime.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21920983 and 21921001.

It is not a weakly prime, because it can be changed into another prime (21921817) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10960508 + 10960509.

It is an arithmetic number, because the mean of its divisors is an integer number (10960509).

Almost surely, 2^21921017 is an apocalyptic number.

It is an amenable number.

21921017 is a deficient number, since it is larger than the sum of its proper divisors (1).

21921017 is an equidigital number, since it uses as much as digits as its factorization.

21921017 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 252, while the sum is 23.

The square root of 21921017 is about 4681.9885732453. The cubic root of 21921017 is about 279.8682075345.

Adding to 21921017 its reverse (71012912), we get a palindrome (92933929).

The spelling of 21921017 in words is "twenty-one million, nine hundred twenty-one thousand, seventeen".