21515767723 has 2 divisors, whose sum is σ = 21515767724. Its totient is φ = 21515767722.

The previous prime is 21515767717. The next prime is 21515767727. The reversal of 21515767723 is 32776751512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21515767723 - 2⁹ = 21515767211 is a prime.

It is not a weakly prime, because it can be changed into another prime (21515767727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10757883861 + 10757883862.

It is an arithmetic number, because the mean of its divisors is an integer number (10757883862).

Almost surely, 2^21515767723 is an apocalyptic number.

21515767723 is a deficient number, since it is larger than the sum of its proper divisors (1).

21515767723 is an equidigital number, since it uses as much as digits as its factorization.

21515767723 is an evil number, because the sum of its binary digits is even.

The product of its digits is 617400, while the sum is 46.

The spelling of 21515767723 in words is "twenty-one billion, five hundred fifteen million, seven hundred sixty-seven thousand, seven hundred twenty-three".