20646 has 24 divisors (see below), whose sum is σ = 47424. Its totient is φ = 6480.

The previous prime is 20641. The next prime is 20663. The reversal of 20646 is 64602.

20646 is a `hidden beast` number, since 20 + 646 = 666.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is an Ulam number.

It is a plaindrome in base 11.

It is a nialpdrome in base 13.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20641) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 540 + ... + 576.

It is an arithmetic number, because the mean of its divisors is an integer number (1976).

2²⁰⁶⁴⁶ is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 20646, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23712).

20646 is an abundant number, since it is smaller than the sum of its proper divisors (26778).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

20646 is a wasteful number, since it uses less digits than its factorization.

20646 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 76 (or 73 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 18.

The square root of 20646 is about 143.6871601779. The cubic root of 20646 is about 27.4333371555.

Subtracting 20646 from its reverse (64602), we obtain a triangular number (43956 = T₂₉₆).

It can be divided in two parts, 206 and 46, that added together give a palindrome (252).

The spelling of 20646 in words is "twenty thousand, six hundred forty-six".