21154568717 has 4 divisors (see below), whose sum is σ = 21155284380. Its totient is φ = 21153853056.

The previous prime is 21154568713. The next prime is 21154568719. The reversal of 21154568717 is 71786545112.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 6450338596 + 14704230121 = 80314^2 + 121261^2 .

It is a cyclic number.

It is not a de Polignac number, because 21154568717 - 2² = 21154568713 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21154568713) 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 in 3 ways as a sum of consecutive naturals, for example, 311492 + ... + 373277.

It is an arithmetic number, because the mean of its divisors is an integer number (5288821095).

Almost surely, 2^21154568717 is an apocalyptic number.

It is an amenable number.

21154568717 is a deficient number, since it is larger than the sum of its proper divisors (715663).

21154568717 is an equidigital number, since it uses as much as digits as its factorization.

21154568717 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 715662.

The product of its digits is 470400, while the sum is 47.

The spelling of 21154568717 in words is "twenty-one billion, one hundred fifty-four million, five hundred sixty-eight thousand, seven hundred seventeen".