21561215717 has 8 divisors (see below), whose sum is σ = 21652482816. Its totient is φ = 21470006272.

The previous prime is 21561215707. The next prime is 21561215743. The reversal of 21561215717 is 71751216512.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21561215717 - 2²⁴ = 21544438501 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 (21561215707) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 841388 + ... + 866634.

It is an arithmetic number, because the mean of its divisors is an integer number (2706560352).

Almost surely, 2^21561215717 is an apocalyptic number.

It is an amenable number.

21561215717 is a deficient number, since it is larger than the sum of its proper divisors (91267099).

21561215717 is a wasteful number, since it uses less digits than its factorization.

21561215717 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 28827.

The product of its digits is 29400, while the sum is 38.

The spelling of 21561215717 in words is "twenty-one billion, five hundred sixty-one million, two hundred fifteen thousand, seven hundred seventeen".