20685643 has 4 divisors (see below), whose sum is σ = 22566168. Its totient is φ = 18805120.

The previous prime is 20685631. The next prime is 20685653. The reversal of 20685643 is 34658602.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 20685643 - 2⁹ = 20685131 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 20685599 and 20685608.

It is not an unprimeable number, because it can be changed into a prime (20685653) 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, 940246 + ... + 940267.

It is an arithmetic number, because the mean of its divisors is an integer number (5641542).

Almost surely, 2^20685643 is an apocalyptic number.

20685643 is a deficient number, since it is larger than the sum of its proper divisors (1880525).

20685643 is a wasteful number, since it uses less digits than its factorization.

20685643 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1880524.

The product of its (nonzero) digits is 34560, while the sum is 34.

The square root of 20685643 is about 4548.1472051815. The cubic root of 20685643 is about 274.5088445209.

It can be divided in two parts, 206 and 85643, that added together give a square (85849 = 293²).

The spelling of 20685643 in words is "twenty million, six hundred eighty-five thousand, six hundred forty-three".