21256476655 has 4 divisors (see below), whose sum is σ = 25507771992. Its totient is φ = 17005181320.

The previous prime is 21256476649. The next prime is 21256476701. The reversal of 21256476655 is 55667465212.

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

It is not a de Polignac number, because 21256476655 - 2²³ = 21248088047 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21256476599 and 21256476608.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2125647661 + ... + 2125647670.

It is an arithmetic number, because the mean of its divisors is an integer number (6376942998).

Almost surely, 2^21256476655 is an apocalyptic number.

21256476655 is a deficient number, since it is larger than the sum of its proper divisors (4251295337).

21256476655 is an equidigital number, since it uses as much as digits as its factorization.

21256476655 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4251295336.

The product of its digits is 3024000, while the sum is 49.

The spelling of 21256476655 in words is "twenty-one billion, two hundred fifty-six million, four hundred seventy-six thousand, six hundred fifty-five".