21957989 has 2 divisors, whose sum is σ = 21957990. Its totient is φ = 21957988.

The previous prime is 21957979. The next prime is 21957997. The reversal of 21957989 is 98975912.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14212900 + 7745089 = 3770^2 + 2783^2 .

It is a cyclic number.

It is not a de Polignac number, because 21957989 - 2⁴ = 21957973 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21957979) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10978994 + 10978995.

It is an arithmetic number, because the mean of its divisors is an integer number (10978995).

Almost surely, 2^21957989 is an apocalyptic number.

It is an amenable number.

21957989 is a deficient number, since it is larger than the sum of its proper divisors (1).

21957989 is an equidigital number, since it uses as much as digits as its factorization.

21957989 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 408240, while the sum is 50.

The square root of 21957989 is about 4685.9352321602. The cubic root of 21957989 is about 280.0254611201.

The spelling of 21957989 in words is "twenty-one million, nine hundred fifty-seven thousand, nine hundred eighty-nine".