21205605655 has 32 divisors (see below), whose sum is σ = 27992563200. Its totient is φ = 15325663872.

The previous prime is 21205605647. The next prime is 21205605679. The reversal of 21205605655 is 55650650212.

It is a cyclic number.

It is not a de Polignac number, because 21205605655 - 2³ = 21205605647 is a prime.

It is a super-2 number, since 2×21205605655² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 858366 + ... + 882724.

It is an arithmetic number, because the mean of its divisors is an integer number (874767600).

Almost surely, 2^21205605655 is an apocalyptic number.

21205605655 is a deficient number, since it is larger than the sum of its proper divisors (6786957545).

21205605655 is a wasteful number, since it uses less digits than its factorization.

21205605655 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 24663.

The product of its (nonzero) digits is 90000, while the sum is 37.

The spelling of 21205605655 in words is "twenty-one billion, two hundred five million, six hundred five thousand, six hundred fifty-five".