21742640921 has 2 divisors, whose sum is σ = 21742640922. Its totient is φ = 21742640920.

The previous prime is 21742640867. The next prime is 21742640951. The reversal of 21742640921 is 12904624712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20260390921 + 1482250000 = 142339^2 + 38500^2 .

It is a cyclic number.

It is not a de Polignac number, because 21742640921 - 2³⁴ = 4562771737 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21742640951) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10871320460 + 10871320461.

It is an arithmetic number, because the mean of its divisors is an integer number (10871320461).

Almost surely, 2^21742640921 is an apocalyptic number.

It is an amenable number.

21742640921 is a deficient number, since it is larger than the sum of its proper divisors (1).

21742640921 is an equidigital number, since it uses as much as digits as its factorization.

21742640921 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 48384, while the sum is 38.

The spelling of 21742640921 in words is "twenty-one billion, seven hundred forty-two million, six hundred forty thousand, nine hundred twenty-one".