21943021 has 2 divisors, whose sum is σ = 21943022. Its totient is φ = 21943020.

The previous prime is 21943013. The next prime is 21943027. The reversal of 21943021 is 12034912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19236996 + 2706025 = 4386^2 + 1645^2 .

It is a cyclic number.

It is not a de Polignac number, because 21943021 - 2³ = 21943013 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21942983 and 21943001.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21943027) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10971510 + 10971511.

It is an arithmetic number, because the mean of its divisors is an integer number (10971511).

Almost surely, 2^21943021 is an apocalyptic number.

It is an amenable number.

21943021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21943021 is an equidigital number, since it uses as much as digits as its factorization.

21943021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 432, while the sum is 22.

The square root of 21943021 is about 4684.3378400794. The cubic root of 21943021 is about 279.9618187734.

Adding to 21943021 its reverse (12034912), we get a palindrome (33977933).

The spelling of 21943021 in words is "twenty-one million, nine hundred forty-three thousand, twenty-one".