21206715823 has 2 divisors, whose sum is σ = 21206715824. Its totient is φ = 21206715822.

The previous prime is 21206715809. The next prime is 21206715833. The reversal of 21206715823 is 32851760212.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21206715823 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21206715833) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10603357911 + 10603357912.

It is an arithmetic number, because the mean of its divisors is an integer number (10603357912).

Almost surely, 2^21206715823 is an apocalyptic number.

21206715823 is a deficient number, since it is larger than the sum of its proper divisors (1).

21206715823 is an equidigital number, since it uses as much as digits as its factorization.

21206715823 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 40320, while the sum is 37.

The spelling of 21206715823 in words is "twenty-one billion, two hundred six million, seven hundred fifteen thousand, eight hundred twenty-three".