20644681 has 4 divisors (see below), whose sum is σ = 21859092. Its totient is φ = 19430272.

The previous prime is 20644649. The next prime is 20644693. The reversal of 20644681 is 18644602.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 18644602 = 2 ⋅9322301.

It can be written as a sum of positive squares in 2 ways, for example, as 13801225 + 6843456 = 3715^2 + 2616^2 .

It is a cyclic number.

It is not a de Polignac number, because 20644681 - 2⁵ = 20644649 is a prime.

It is a super-2 number, since 2×20644681² = 852405707183522, which contains 22 as substring.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20644081) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 607180 + ... + 607213.

It is an arithmetic number, because the mean of its divisors is an integer number (5464773).

Almost surely, 2^20644681 is an apocalyptic number.

It is an amenable number.

20644681 is a deficient number, since it is larger than the sum of its proper divisors (1214411).

20644681 is a wasteful number, since it uses less digits than its factorization.

20644681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1214410.

The product of its (nonzero) digits is 9216, while the sum is 31.

The square root of 20644681 is about 4543.6418212707. The cubic root of 20644681 is about 274.3275293676.

The spelling of 20644681 in words is "twenty million, six hundred forty-four thousand, six hundred eighty-one".