21724076021 has 2 divisors, whose sum is σ = 21724076022. Its totient is φ = 21724076020.

The previous prime is 21724075981. The next prime is 21724076039. The reversal of 21724076021 is 12067042712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17979859921 + 3744216100 = 134089^2 + 61190^2 .

It is a cyclic number.

It is not a de Polignac number, because 21724076021 - 2¹⁸ = 21723813877 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21724076051) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10862038010 + 10862038011.

It is an arithmetic number, because the mean of its divisors is an integer number (10862038011).

Almost surely, 2^21724076021 is an apocalyptic number.

It is an amenable number.

21724076021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21724076021 is an equidigital number, since it uses as much as digits as its factorization.

21724076021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 9408, while the sum is 32.

The spelling of 21724076021 in words is "twenty-one billion, seven hundred twenty-four million, seventy-six thousand, twenty-one".