21813907681 has 4 divisors (see below), whose sum is σ = 21815264452. Its totient is φ = 21812550912.

The previous prime is 21813907679. The next prime is 21813907711. The reversal of 21813907681 is 18670931812.

It is a happy number.

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

It can be written as a sum of positive squares in 2 ways, for example, as 9323833600 + 12490074081 = 96560^2 + 111759^2 .

It is a cyclic number.

It is not a de Polignac number, because 21813907681 - 2¹ = 21813907679 is a prime.

It is a super-2 number, since 2×21813907681² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21813907651) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 653976 + ... + 686521.

It is an arithmetic number, because the mean of its divisors is an integer number (5453816113).

Almost surely, 2^21813907681 is an apocalyptic number.

It is an amenable number.

21813907681 is a deficient number, since it is larger than the sum of its proper divisors (1356771).

21813907681 is a wasteful number, since it uses less digits than its factorization.

21813907681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1356770.

The product of its (nonzero) digits is 145152, while the sum is 46.

The spelling of 21813907681 in words is "twenty-one billion, eight hundred thirteen million, nine hundred seven thousand, six hundred eighty-one".