21556642655 has 4 divisors (see below), whose sum is σ = 25867971192. Its totient is φ = 17245314120.

The previous prime is 21556642649. The next prime is 21556642661. The reversal of 21556642655 is 55624665512.

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

It is an interprime number because it is at equal distance from previous prime (21556642649) and next prime (21556642661).

It is not a de Polignac number, because 21556642655 - 2²⁰ = 21555594079 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2155664261 + ... + 2155664270.

It is an arithmetic number, because the mean of its divisors is an integer number (6466992798).

Almost surely, 2^21556642655 is an apocalyptic number.

21556642655 is a deficient number, since it is larger than the sum of its proper divisors (4311328537).

21556642655 is an equidigital number, since it uses as much as digits as its factorization.

21556642655 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4311328536.

The product of its digits is 2160000, while the sum is 47.

The spelling of 21556642655 in words is "twenty-one billion, five hundred fifty-six million, six hundred forty-two thousand, six hundred fifty-five".