21691758655 has 16 divisors (see below), whose sum is σ = 29767150080. Its totient is φ = 14865122592.

The previous prime is 21691758631. The next prime is 21691758659. The reversal of 21691758655 is 55685719612.

It is a cyclic number.

It is not a de Polignac number, because 21691758655 - 2²³ = 21683370047 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21691758596 and 21691758605.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21691758659) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 134739 + ... + 248068.

It is an arithmetic number, because the mean of its divisors is an integer number (1860446880).

Almost surely, 2^21691758655 is an apocalyptic number.

21691758655 is a deficient number, since it is larger than the sum of its proper divisors (8075391425).

21691758655 is a wasteful number, since it uses less digits than its factorization.

21691758655 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 384438.

The product of its digits is 4536000, while the sum is 55.

It can be divided in two parts, 216917 and 58655, that added together give a palindrome (275572).

The spelling of 21691758655 in words is "twenty-one billion, six hundred ninety-one million, seven hundred fifty-eight thousand, six hundred fifty-five".