21705015561 has 8 divisors (see below), whose sum is σ = 28970584224. Its totient is φ = 14454728640.

The previous prime is 21705015539. The next prime is 21705015569. The reversal of 21705015561 is 16551050712.

It is a happy number.

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

It is not a de Polignac number, because 21705015561 - 2¹⁷ = 21704884489 is a prime.

It is a super-2 number, since 2×21705015561² (a number of 21 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21705015569) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3817120 + ... + 3822801.

It is an arithmetic number, because the mean of its divisors is an integer number (3621323028).

Almost surely, 2^21705015561 is an apocalyptic number.

It is an amenable number.

21705015561 is a deficient number, since it is larger than the sum of its proper divisors (7265568663).

21705015561 is an equidigital number, since it uses as much as digits as its factorization.

21705015561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7640871.

The product of its (nonzero) digits is 10500, while the sum is 33.

The spelling of 21705015561 in words is "twenty-one billion, seven hundred five million, fifteen thousand, five hundred sixty-one".