21565718655 has 16 divisors (see below), whose sum is σ = 37159392480. Its totient is φ = 10616969088.

The previous prime is 21565718653. The next prime is 21565718687. The reversal of 21565718655 is 55681756512.

It is a happy number.

It is not a de Polignac number, because 21565718655 - 2¹ = 21565718653 is a prime.

It is a super-2 number, since 2×21565718655² (a number of 21 digits) contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21565718598 and 21565718607.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21565718651) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 55296520 + ... + 55296909.

It is an arithmetic number, because the mean of its divisors is an integer number (2322462030).

Almost surely, 2^21565718655 is an apocalyptic number.

21565718655 is a deficient number, since it is larger than the sum of its proper divisors (15593673825).

21565718655 is a wasteful number, since it uses less digits than its factorization.

21565718655 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 110593450.

The product of its digits is 2520000, while the sum is 51.

The spelling of 21565718655 in words is "twenty-one billion, five hundred sixty-five million, seven hundred eighteen thousand, six hundred fifty-five".