21655515561 has 8 divisors (see below), whose sum is σ = 28900202880. Its totient is φ = 14423919312.

The previous prime is 21655515559. The next prime is 21655515577. The reversal of 21655515561 is 16551555612.

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

It is not a de Polignac number, because 21655515561 - 2¹ = 21655515559 is a prime.

It is a super-2 number, since 2×21655515561² (a number of 21 digits) contains 22 as substring.

It is a Smith number, since the sum of its digits (42) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21655511561) 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, 3268906 + ... + 3275523.

It is an arithmetic number, because the mean of its divisors is an integer number (3612525360).

Almost surely, 2^21655515561 is an apocalyptic number.

It is an amenable number.

21655515561 is a deficient number, since it is larger than the sum of its proper divisors (7244687319).

21655515561 is a wasteful number, since it uses less digits than its factorization.

21655515561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6545535.

The product of its digits is 225000, while the sum is 42.

The spelling of 21655515561 in words is "twenty-one billion, six hundred fifty-five million, five hundred fifteen thousand, five hundred sixty-one".